Foo’s guide to butt sex

Recently, every time I’m about to engage in butt sex I think to myself that I should write some kind of guide. Not because I consider myself a particularly skilled practitioner but because I remember when I was starting out I had a lot of confusion that a really good guide could have helped alleviate.

There have been things I worried about for years which turned out to be no big deal, and things I have done wrong for over a decade which I only learnt recently. I hope some of this gathered intel could be helpful to you. As a young gay man in my 20’s I could certainly have used some of this information!


What is butt sex?

Let’s not get too prescriptive, but for the purposes of this post my definition of butt sex is where a penis penetrates a butt. There are other sex acts which can involve a butt, which come under the term “anal play”. Things like fingering, toys, vibrator play, eStim, rimming. This post is all about the simple act of penis in butt.


You may notice that I use they/them pronouns in this. That’s because anyone could enjoy butt sex. Anyone could have a penis and/or prostate. Better to just use gender neutral pronouns than to exclude anyone.


People surprisingly get confused and it may seem a bit silly but honestly being precise in your language is very important. You don’t want to give people the wrong expectations when you’re talking about sex.

Top – this is the person who plays the penetrative role. Their penis / cock is going into the other person.

Bottom – this is the person who is penetrated. The cock goes inside them. In this instance we’re talking about cock in the butt, but cock can go in many places.

Vers – versatile, happy to play either top or bottom role.

Dom – this is the dominant person, easiest way to think about this is this person is the one who decides what happens next – they are in control.

Sub – this is the submissive person, they are the one who lets the other person decide what happens next. Important to note here the word “lets” even though the sub is submissive, the sub still chooses to “let” the dom be dominant.

Switch – happy to play either dom or sub role, sometimes in the same session.

Although it’s common for the bottom to be the sub and the top to be the dom, it can be a lot of fun to mix it up. the term “Power bottom” refers to the person who takes charge while being penetrated, often in a reverse cowgirl position (more on that later).

I have heard people get confused and say “I was subbing from the top” when they meant “I was the dommy power bottom”. Very important to get the language right to avoid disappointment.


Consent is the most important thing in any kind of sexual activity.

Get consent – before you have sex, ideally quite some time before (like days before), make sure that you actually discuss what kinds of things you want to do to each other, who is comfortable with what roles and (of course) whether you want to have sex in the first place. Are you both versatile switches? Is one of you more dominant? Who is hankering after being the bottom? Who is in the mood to top?

Listen for consent withdrawal – if at any point any party withdraws their consent you stop immediately. I really don’t care how much fun you’re having. It stops immediately and you check on them. Remember also that some people talk a big game online and then change in person. Someone might have been keen to bend you over the kitchen table while chatting online, but once you meet in person they only want a cuddle. People are allowed to change their minds.

No drunk sex – I recommend you just don’t do drunk sex, it’s not worth the uncertainty of knowing if the other party was consenting. Sure, after a glass of wine, you could consent, but you can’t make that judgement as to whether someone is “drunk” or “tipy” unless you know them very well.

No surprise buttsex – there’s no such thing as consensually going into someone’s butt when they didn’t expect it. There’s all kinds of kinky play you could get up to (out of the scope of this post) but that all requires even more consent, not less. You need someone to be clear that they specifically want your cock specifically in their butt.

Sexy consent – How do you make consent sexy you might ask? Well, consent is sexy regardless but you can make consent into something quite fun just by using words. Let’s say you’re busy making out with someone and you say:

I’m going to throw you onto the bed and fuck your tight little butt till you’re moaning with pleasure. Do you want that?

The response you’re looking for is “yes”. Not a shy blush or a batting of the eyelids, but a “yes”. If you still don’t get it, you can follow up a bit more explicitly “I’m going to need an answer” or something like that. Verbal enthusiastic consent is what you’re after.

If you’re the bottom you might equally say:

I want you to rail me all night tonight, do you think you could do that for me?

Once again, you want a clear “yes”.

Of course, once you know someone very well and have been having sex for a while, you will probably have a short hand way of doing this, but even well established partners have ways of clearly establishing consent for sex. Please don’t assume you can “tell what someone wants” unless they tell you.

Protection / safe sex

By default, practice safe sex. This involves a condom and lube. You don’t need fancy extra thick condoms. Ordinary condoms are fine, but please don’t use any of the weird extra thin ones, they will not survive buttsex.

For lube, I recommend an ordinary silicone based lube. Some prefer oil. I think silicon lasts longer but that’s a preference. Make sure you use a lot, especially when you’re just starting out.

HIV is not the only thing you are looking to prevent with condom usage and it’s not just a gay thing. If you’re having buttsex, you need a condom and lube.

Some couples practice unprotected buttsex and that’s up to them but they will have communicated up front what they plan to do, how they plan to do it, understand the risks and are completely honest about other sexual partners. In my opinion unprotected anal sex makes sense with long term partners who have a great deal of trust. Even then, I have heard all kinds of stories of long term partners giving each other diseases by cheating, so please be safe.

Deciding who is in control

Deciding who is top and who is bottom as well as who is sub and who is dom can actually be a little tricky. If you’re at the point where you’re having sex you would ideally have discussed these preferences up front. I think it’s very important to establish who is comfortable performing what roles.

If you don’t personally have a preference and you’re in the thick of things, then I think the least jarring way to figure all this out is for you to assume that you are the dom. You take a bit of a dominant position over the person and whisper in their ear “so what shall we get up to?”

If they’d prefer to dom, this is the point where they will say “I’m going to xyz, would you like that?”, you can then choose to agree to this (with a nice clear “yes please” / “sounds good to me”) or to propose an alternative.

Alternatively, they may meekly suggest a submissive role for themselves “I really want to feel you inside me” or “I’d like to try topping please” or whatever.

If you have a role for yourself in mind, then make sure you vocalise this. Few things are more frustrating than not knowing what the other person wants. Be clear “I want to feel you inside me” or “I want to be inside you so bad” or something like that. Check for consent.

If you’re not getting a clear message, then there’s no harm in actually taking a time out to discuss who wants what. If the other person is not mature or sure enough to tell you what they want to try, then they are not ready to consent. Stop.

Advice for bottoms

Being a versatile switch with a preference for bottom, I thought I’d start here.

Don’t wipe too hard

The very best advice my doctor ever gave me was “don’t wipe so hard!” In general, I think we all wipe too hard, this can damage the sensitive skin around your anus and in the worst case cause bleeding, which makes sex uncomfortable. My advice is to lightly wipe to clear the area and then irrigate with a shower afterwards.

Fiber supplements

This is so very important: you probably don’t get enough fiber in your diet. Talk to any proctologist and they will tell you to have more fiber. I have two teaspoons of Metamucil every meal.

I used to think fiber was a kind of rough stuff which scraped the insides of your butt. Not at all! Fiber helps bind poop together yes, but it is also gloopy and lubricates your butt as well. You need more fiber and don’t rely on getting it from food, go buy a suppliment right away!


Probably the biggest concern an inexperienced bottom has is poop. For starters please understand that the top knows that poop comes out of your butt, so please try not to get too wound up about this particular thing. If poop happens, you will deal with it.

Apart from sight and smell, the reason you don’t want poop involved in sex is it makes it physically uncomfortable, it acts a bit like “grit” in your butt and can cause friction for both you and the top. Depending on the nature of the sex it can actually bring a halt to sex pretty quickly 0/10 would not recommend.

So, how to rid yourself of poop?

First thing to remember is that most of the time your butt doesn’t have poop in it at all. Butt sex is confined to the rectum, which is below your colon, poop only resides here for a short time between having been processed by your body and the time you poop. For most people, having a bowel movement (taking a dump) about an hour before sex is all you have to do. Remember to be gentle wiping (see “don’t wipe so hard”). I usually make a point of going to the toilet about 1 hour to 30 minutes before sex.

As a follow-up what I do is put a condom on my finger, cover it with a bit of lube and stick it up there.

Let me pause for a bit while that sinks in (hehe).

Yes, that’s right, I am advocating you stick your finger (with a condom on) in your ass.

If you’re squeamish about this, I invite you to think about what you’re hoping is going to happen to your butt in the next hour or so: you are hoping someone else is going to stick their cock in there. Would you rather they found the poop with their cock instead? Yes, I thought so, now stick your finger in as far as it can go and feel around for poop.

If your finger came out clean and you didn’t feel any discomfort / poop then congratulations! You’re all set and you’ve also loosened yourself up a little as a bonus.

What if there’s poop on your finger? Well, if your last bowel movement didn’t manage to get it out, it probably needs a little help. If it’s relatively firm, I’d just encourage you to scoop it out with your finger while you squeeze with your butt. Now is not the time to get precious. That poop is in the way of sex and you just need to get rid of it. Scoop it out, it feels super weird and might take a few attempts but trust me, it’s a better feeling than sex with poop in your butt.

Make sure you use a shower or toilet paper with some water to clean the outside of your butt afterwards.

Some people like to use a douche, and this can help too, but I personally find that I can overdo it, and this then turns solid poop into brown liquid which is not fun at all. Your mileage may vary.

If your poop is super runny, this is probably worst case poop scenario. I would encourage you to persist with the finger method a few times, maybe with the assistance of a shower to irrigate as much as possible. You could try a douche, but that risks creating a soupy mess. I find that after a few attempts with a finger, you’ll end up with it coming out clean in the end. That’s all you’re after at the end of the day.

Stretching / Toy use

Some people think that they need to stretch their ass or practice before butt sex. This is partly true. Using a toy in your butt regularly can help with butt sex, but it’s mostly for psychological reasons. If you are tense during butt sex you can unintentionally keep your butt hole clenched, this can cause discomfort or even damage if you’re not careful. Using a toy can help you relax more and feel more comfortable getting things in there.

Unless you keep a toy in there for days on end, you are not going to over-stretch your butt. People don’t get “loose” just due to normal amounts of anal play.

I recommend you insert a toy before every sexual encounter. I prefer to do this myself beforehand so I can control the situation. Using a toy beforehand is also a good way to double check that there’s no poop deeper in your butt. A “soft” “Winston’s tail” from Bad Dragon is a great toy for this particular job, it’s highly tapered and unlikely to pose too much of a challenge.


I have never found the need for drugs to enhance sexual performance and I have had no trouble with some rather big and challenging people. No judgement from me, but I encourage you to remember that it’s all about being relaxed and the right frame of mind, not some kind of chemical enhancement.


This is one of the most important things during sex. The best thing the top can hear is “yes” plus some moaning. If they’re railing you, and you are enjoying it, or you want them to carry on going say “yes” as much as you can.

Be vocal, give them an indication that you’re enjoying things, If you’re not enjoying things, then mention things they can change. The kinds of things that are normal to say during sex are:

  • “Please, yes, yes, yes”
  • “Hey can we have more lube?”
  • “I wanna try on my back/front please”
  • “Slower please”
  • “Faster!”
  • “I want you to cum”
  • “Oh you’re so big / nice / hard / etc”
  • “Stop, I need a break”

and so on

Things you should avoid:

  • “Are you in yet?”
  • “Are you almost done?”
  • “You can’t cum tonight can you?”
  • “Oh no, you’re too soft!”
  • “Having trouble are we?”

or anything making fun of or belittling their efforts (unless they have told you up front that’s what they want to hear because they get off on that kind of thing). Your job is to appreciate their efforts, I mean you went through all that trouble to enjoy them after all!

If the condom breaks, you will probably feel it snap. When this happens, the temptation is to keep going. The better thing to do is stop, check, get a new condom and also get tested the next day. Got to be respectful and responsible.

Getting off

You are both responsible for your own orgasm. The top is there to obviously stimulate you in the butt, but at the end of the day, their responsibility is to fuck you and to look after their own orgasm. Not everyone is skilled enough (or willing) to deal to the bottom’s orgasm at the same time. For this reason, I recommend that while the top is going at it, you play with yourself. If the top is dominant and tells you that they want to be in charge of that, then let them of course.

Because you get very sensitive shortly after cumming, I recommend the top cums first, you don’t want to have to ask them to stop just because of that.

You may opt not to cum at all during buttsex, chances are the top will get you release once they have had their turn, that’s often how these things go. You are entitled to ask for things, even if you are the sub. You can say things like “I wanna cum please” for example. If you truly are in a sub role and they are in the dom role, then whether you get to cum is up to them.

Dealing with soft cocks

Sometimes people go floppy and can’t get hard. This is almost always psychological. Don’t bring attention to it, just gently grab the cock and get it hard with a little attention. Different people need different things to get hard. Some things to try:

  • rubbing the nipples or ears can work for some people
  • getting them to perform oral sex on you can arouse some people (for this reason, 69 is a good play option for inexperienced tops)
  • you performing oral sex on them
  • kissing
  • verbal encouragement “oh man, this looks and feels so great, you’re so sexy”

Dealing with inexperienced tops

Inexperienced tops can be fun and exciting but also a little tricky because they don’t know how hard is too hard, nor where or how to start. I recommend that with an inexperienced top, you start with them lying on their back and you in the “cowgirl position (facing them). This way you can feed their cock into your butt and control the whole scenario. Just remember that most people can’t cum this way, so you will have to graduate to doggy-style if you want them to cum.

Advice for tops

Dealing with floppy cock

So the worst thing happens. You are about to go in and you go soft. Just remember that this is entirely common, emotional and mostly in your head. Unless age or alcohol is a factor, you are most likely just nervous. I have had floppy moments mostly when it’s someone I am super excited about having sex with. For me, the more pressure I have, the more likely I am to be soft.

The trick here is to make it the bottom’s problem. Take the condom off and say “right, I need your lips around this” or something like that. Throw them on their back and suck them off for a bit if that’s what gets you hard. You should know what excites you. Remember, sex is a team sport and the bottom wants to play their part. They want you to be hard almost as much as you do.

If you can’t get hard at all, then don’t make a big deal about it, turn your attention to the bottom and give them a lot of attention. Giving them attention makes them feel good and also gives you time to work up your own arousal.

Premature ejaculation

So, the worst thing happens. You get one inch of yourself in and the excitement just takes over and you cum instantly.

Don’t say “sorry”. The bottom doesn’t want to hear sorry. The bottom wants to hear “OMG, you’re so hot, I just came, ugh”. So say that instead.

If you say “sorry” and start obsessing about how fast you came, you make it all about you. Make it instead all about them. Make it all about how much they turn you on and how much they drove you over the edge.

The bottom wants you to collapse on them and smother them in passionate kisses, and then give them a hand job or blow job for their trouble. Trust me, they are not even going to remember how long you took to cum if you make the rest of the evening all about them.

Whenever someone cums quickly, I am usually super flattered. If you follow it up with a lot of attention for the bottom, you can turn what might feel like a disappointing evening into “best sex ever”.

Taking too long

So the worst thing happens. You have been going at it for ages, and you just can’t seem to cum. You’re still hard but it just isn’t working. Here are some things to try:

  • Stop worrying about the bottom – I know how it goes “oh no, I am taking too long, what if I am hurting them or they are getting bored, what if they think I’m not having fun, maybe I’m no good at sex”. All of this builds up this block in your mind making it impossible to cum. Stop worrying about the bottom and what they think and focus on you and your pleasure. Grab them by the hips and go to town. Unless they tell you to stop you are expected to be enjoying yourself, so enjoy!
  • Change positions – doggie style seems to be the most consistently successful position I have found
  • Try standing – standing next to the bed while the bottom crouches doggy style can put less pressure on your knees and make it less physically demanding

If all else fails, flip them over onto their back and jerk off onto them or into their mouth or something. Obviously tell them what you are going to do before you do it, so you can get their consent “I’m going to cum in your mouth, is that ok?” Trust me, if you railed them for ages, couldn’t cum and then came all over them instead, they are going to decide you’re some kind of sex god.

If masturbating isn’t doing it for you either, then focus your attention on them. Depending on how much in control you want to be you might say “you know, I’d much rather play with you” or something. After all, you did give them a darn good go.

After ejaculation

Everyone’s different but if you do manage to cum, make sure you let the bottom know. They like to hear that kind of thing. Either say “I’m cumming” or just make sure you’re making an appreciative noise. Feel free to hold them close afterwards and enjoy the afterglow. Don’t be too quick to focus onto their turn. Allow you both to enjoy the afterglow of your orgasm. Trust me, the bottom is enjoying it too.

The bottom’s turn

Convention is that the bottom cums second because after cumming one gets quite sensitive. Once you’ve overcome your afterglow, you can give them a hand job or a blow job. If you’re quite dominant and they’re quite submissive, then you do get to choose if they cum at all, though it is polite to let them cum. If you struggle to get them off (it can happen). Then have no fear, tell them to work on it themselves and instead focus on stimulating them in other ways.

Simultaneous ejaculation

You can try for a near-simultaneous ejaculation which is quite fun. Feel free to tell the bottom to stimulate themselves, keep them informed of how close you are so they can time their own climax.

If you’re particularly experienced, you could get them off yourself while you get off, though I wouldn’t recommend this unless you have full awareness of how your own body works, lest you get them off before yourself.

Don’t let simultaneous ejaculation be the only goal. Trying to time things can be distracting and you really ought to be focused on enjoying each other.

The goal with sex is to have the sex and feel the intimacy, everyone is different and everyone wants something different out of sex. Exploring those differences (and each other) is part of the fun.

A song about foxes

I’ve heard it said, that the fox is the sluttier  
just like to add this one thing that’s been on my  
stereotype is such a bad thing to  
listen up and I’ll straighten record for  

just ‘cos we’re  
don’t mean we’re  
foxes will  
love you for  

Love, love  
love, pull the tail right  
might raise a  
tail or two,
But just like the  
Foxes are  
loyal for  

Please don’t assume that I have been lying to  
fox will bend over for a guy who’s named rover, or  

hung like the  
ly pillow  
foxes will  
love you for  
Love love  
love, collar, leash and  
take just what we can  
but I have not yet  
fox who has  
had quite  

so my friend here I come to the serious  
secret truth that I should have said from the  
While you’re  
putting your  
all of them  
filling the  
holes in their  

Love, Love,  
Love, Never quite  
While you’re  
panting and  
lying there  
make him your  
foxie for  

Love, Love,  

Detecting buttsex

You will recall that in my initial sensing application I failed to check to see if I could detect buttsex. Well, I am pleased to report that I have progressed somewhat from that! It took a while for me to work up the nerve, because my mold is a little thick and it’s been a while, if you know what I mean.

Anyway, science and a little boredom gave me the opportunity to test the insertable toy with all three gestures I wanted to detect.

You may recall that a hand job is quite unique with very clear signals from all of the sensors:

Hand job raw sensing data.

What is especially unique about the hand job is typically the hand can’t stimulate the entire shaft when it’s fully “in” this results in the tip of the toy poking out of your hand. Even if you had a particularly large hand, i would hazard that because of the shape of your hand, the tip would still lose stimulus at the peak of the “in” stroke.

A blow job is similar except that the tip gets stimulated in varied and complex ways when it enters the mouth, likely due to saliva. Also, I personally wasn’t about to uniformly stimulate the base of the shaft with my mouth alone.

Raw sensing data during a blow job.

Finally, the data you have all been waiting for. Insertion into the butt looks like so:

Raw data sensing in the butt.

Note that it’s a very different story to the previous two data sets. the tip is stimulated on entry and is essentially always stimulated throughout. This is even when I withdrew it as far as I dared. I think this is because even when it’s no longer inserted, your body is still close enough to the device to act as a capacitive body, even without direct contact or pressure.

With the above data I was able to crudely detect the difference between a hand job and butt stuff using the DTW algorithm “most of the time”. Evidence suggests I will need to improve my normalisation algorithm because in cases where a dataset is “flat” (e.g. as in the butt stuff), the normalisation tends to unnecessarily amplify noise, which can result in false positives. I also suspect that the 8 point moving average might be a little too aggressive.

Detecting cum with voltammetry

After my little stint of research, I set about putting the theory into practice. Before I go into it, here is a video of detection working (warning, contains bodily fluids).

Warning, this video contains bodily fluids.

Fluids in order: water, lube, salt water, urine, semen.

My laptop keyboard still has suspicious fluids on it…

Please note the above video is a best case scenario and a lot of testing is still required!

My first attempt was to just pass 5v into various samples and see what they did. I used the #2 digital output pin on the Arduino to control whether or not any power was sent to the sample and a 10 kΩ shunt resistor so I could measure the current across the sample by reading the A0 analog in for the Arduino. I measured the current once every 10 ms for 2 seconds, then rested the sample for 2 seconds.

The results were encouraging.

The graph below shows one round of stimulation of a sample of water, the orange line represents voltage in (5v) and the blue line is the current measurement. You can see I rest the sample between trials for 2 seconds (important).

Change in current over time when sending 5v through water.

The following shows the change in current measured in a sample of cum.

Change in current over time when sending 5v through cum.

So, there’s definitely something happening, the current across the sample is changing for the duration of the stimulation (2 seconds), but how to get a more meaningful comparison? I knew that I needed at least 1.23 v to electrolise water into into oxygen and hydrogen, but I didn’t want to use much more than that. I used a simple voltage divider made from two 22 k Ω resistors, resulting in something close to 1.8 v across the sample, which seemed to work OK.

Apologies to electrical engineers who are offended by my poor diagram.

After taking many samples and calculating an average for each sample, I could say with confidence that on average, a 2 second stimulation of the various samples looks like this:

Average change in current over time for different samples.

Now, it looks pretty cut & dry: cum has on average a much much lower final current after 2 seconds. Why not just measure the current value after 2 seconds of stimulation and if it’s below a threshold (say 35 in the example above), then it’s cum? Well, the problem is that this is an average, the real data is a whole lot messier:

Change in current over time, just for the cum sample. There’s a wide variety of data points.

Change in current over time for the urine sample only.

The fact that cum has a very distinctive “shape” on the average graph gave me the encouragement to try harder to untangle signal from the noise.

To overcome the variability in the data I did two things: firstly I took a 5 point moving average for all points, to smooth them out a little. I then expressed every set of 5 points as a ratio of the first 5 points. So, to get the value for point 8, I would calculate Average(Points(8-12))/Average(Points(1-5)), which is actually the same as Sum(Points(8-12))/Sum(Points(1-5)).

This resulted in the following graph (once again, taken as an average):

Ratio of the 5 point moving average to the first 5 point moving average.

That’s all very well, but this is still an average, how do we handle the fact that each trial (each time I stimulate a sample) may have variability to it? Looking at the minimum and maximums rather than the averages, we get this:

Minimum and Maximum current ratios.

If you look carefully, you can see at about 10 or 15 (between 100 and 150 ms), there’s a promising gap between all other minimums and the maximum value for cum. I focused my attention on this ratio.

So, that’s it right? If the ratio between the first 5 points and points 10-15 is less than 0.8, we have cum! Well, yes and no. As I said before, by passing a current through the sample, we are actually changing it, so we need to consider how the nature of the sample changes over time. Also, I wanted to speed up the time taken to get a result, up until now, I was stimulating for 2 seconds and resting for 2 seconds, that was quite slow for the detection I wanted.

So, I sped it up, this time allowing the sample to rest only 100 ms and stimulating for only 200. I then recorded the ratio and plotted it over time. So, the graph below is showing many hundreds of trials (a cycle of stimulation and rest for the sample), where the x-axis is the trial number.

Fast sampling over time

Saliva appears to be quite unstable over time. All other samples I used appear to stabilise well above the ratio for cum. Saliva, however, comes dangerously close. To be fair, I don’t mind so much if I get false positives on saliva since I am not expecting saliva to find it’s way inside the masturbator toy.

I am still worried that the samples do change a fair bit over time, making stable readings difficult. I also note that my simple copper electrodes may not be good enough. The positive electrode slowly builds up a black layer of oxidation, probably from the electrolysis.

Simple code for the detector is here: voltammetry2.sdf.ino

Approaches for detecting cum

It’s been referred to as the “holy grail” of teledildonics, and in my hubris, I want to have a go at detecting male ejaculation. Why ejaculation? Well, this is specifically for uses where someone is playing with a male masturbator toy and they climax. Wouldn’t it be great if they got some kind of feedback for their effort? Maybe the game gives them a reward or the content changes somewhat. Without detecting their climax, there’s no way for the system to do so.

Such a detector would need to be:

  • Affordable (let’s say, less than $50 per sensor)
  • Safe (don’t want to give them a nasty shock or chemical burn as they cum)
  • No false negatives (would be disappointing even if it failed to work just once)
  • No false positives for other common fluids (lube, urine, pre-cum, saliva, water and sweat)
  • Nearly immediate – no point in recognising cum some minutes after the event!
  • Robust against environmental factors (like humidity or what they had for dinner)

I set about researching a number of techniques which I thought would bear fruit:

Florescence: The first thought one might have is to do what they do in the movies and use “black light” or UV. From reading this post on the florescence of semen, it turns out that you need Luminol to trigger semen’s fluorescence with UV, though it sill fluoresce under blue light. Besides all that, these fluorescence based tests only appear to work on dry semen, not liquid semen. This fails the “immediate” test.

pH: At between 7 and 8 on the pH scale, semen is slightly basic, but not enough that using a pH sensor is going to give you a distinguishing marker verus, say, tap water. Also, this pH would probably can vary from person to person. Finally, the pH sensors I have seen are rather bulky.

Spectral Analysis: From semen’s spectral response it looks like the 1650 cm-1 wave number range is good for detecting cum. Detection works this way because certain organic compounds in semen vibrate at a certain frequency. These compounds are found in many other organic samples. The problem with this approach is, this frequency is in the mid-range IR, which is very expensive to produce and detect since it’s so close to heat. It would require expensive specialised apparatus to do it this way and it would most likely both destroy the sample and possibly burn your penis in the process.

Resistance: I tried measuring the resistance of cum using various approaches, but just when I thought I understood how it related to other fluids, I got different readings. Besides which, urine (at approximately  70k ohms) is quite a good conductor compared to cum (about 700k ohms).

Electro-chemical: After reading this paper about detecting chemicals. It made sense to me that whatever technique is used to detect glucose in blood or specific ions in solution should be able to work with cum, because I knew cum contained some salts, in particular sodium and potassium ions (see Biochemistry of semen and the Wikipedia page for semen). We were finally getting somewhere!

Voltammetry: A technique known as Voltammetry, passes a known voltage through a sample and observes how the current through the sample changes over time. This recognises the fact that the act of passing a current through a solution will perform some kind of electrolysis on the solution.

Finally, the phenomenon where semen’s resistance changed over time made sense! You see, whenever you pass a current (no matter how small) through a sample such as semen, you are going to change its chemical composition somewhat. We can measure that change by measuring a change in current.

Next, I actually implement a voltammetric apparatus for detecting cum.

Insertable Speed Detection the Easy Way

So, I have gesture detection working relatively well, the next hurdle is speed of the gesture. It sounds like a relatively simple problem to solve, but it’s deceptively complex, especially since we’re dealing with a series of data points.

In the video above, I am using a simple moving average on stream 3 of the input. Whenever the current data point drops below the moving average, that’s considered an “out”, when it drops above, that’s considered an “in”, the result is data that looks something like this:

Every time the blue line crosses the yellow line, we count a “tick”. Speed is the number of ticks in the last 16 samples.

Whenever the data value crosses the moving average in any direction, I consider that a “tick”. I then count the number of ticks in the last n samples to get an average speed during those samples.

It works surprisingly well, you could increase the number of samples to get a smoother speed calculation, but I think a responsive value is better. I am currently summing across 16 ticks.

In theory, a Fast Fourier Transform should be able to give me the frequency of the signal I am recording and that frequency could be used to approximate speed of the “hand job” gesture. In practice, I think the moving average approach is relatively computationally cheap as well as robust.