Reid is quite aware that seminal fluid is made from amino acids, citrate, enzymes, fructose, phosphorylcholine, prostaglandins , proteins, vitamin C and more components. He knows that a healthy ejaculation contains between two hundred and five hundred million sperm. He's also heard that the taste of a person's semen can be affected by their diet.

There is a serious lack of research on the subject, Spencer finds. He understands that, of course; finding participants willing to taste countless samples of semen is not likely to be an easy feat, at least not in a clinical setting.

He's been conducting his own research for almost three months now. He's got a small notebook with at least forty subject notes jotted down, recording various properties of the semen he's encountered; colour, consistency, amount, flavour, and also a little space for extra notes or a personal opinion on the extraction, should he have it.

He'd have liked to be able to more accurately record each parameter, but it was simply not practical to retain a sample for later testing with the appropriate equipment, so his measures have to be value judgements. Bad science, he considers, but the most practical method with his means.

The first recorded sample is his own, when he licks it off his hand after masturbating. It's off-white and has a consistency like PVA glue, and there's what he estimates to be less than a teaspoon of ejaculate. It tastes unpleasant, very bitter. From what he's read he thinks it's because of the excessive amounts of coffee he drink; anecdotal accounts suggest coffee drinker's semen tends to be the least pleasant to encounter orally.

Subsequent samples are easy to obtain. There is no shortage of men and even sex-assigned-male women who patron bars with a large LGBT clientele willing to allow a stranger to perform oral sex on them. Very few of them object to Reid's efficient method and quick departure after, and most are too hazy after their orgasm to notice him extracting his notebook from his pocket as walks away, savouring the semen in his mouth and noting its qualities.

As much as he enjoys his months of collecting anonymous samples – and Reid is a man who enjoys this kind of research immensely – he realises he's missing an element. His original abstract had been to test the effects of diet on seminal flavour, and gathering information on diet from anonymous donors is rather impractical. All he's done so far is document the variance in flavour between unconnected persons with ejaculatory capability. He does not consider the research a waste of time, of course. No science is waste of time, and neither is oral sex.

Finding participants who he has knowledge of their diet seriously reduces his sample pool. He's nothing if not committed, however, and he devises a plan of action to make his able team members supply their semen.

He's rather surprised when the first person he manages to allow to perform oral sex upon him is Hotch. Of course he doesn't share his true reasoning, but he still ends up knelt in front of Hotch as he sits at his desk in his office none the less. Hotch's cock is average in its measurements, but rather impressive; a defined ridge and veins make it look somewhat intimidating, but Spencer has encountered enough penises not to hesitate in the undertaking. He sucks lavishly, savouring the extraction process. He's well practiced and Hotch doesn't seem to have been sucked off for some time, because he extols Reid's talented tongue and ejaculates in under four minutes.

Reid makes sure to take the majority of the release into his mouth, but allows some to land on his closed lips so he can wipe that away with his fingers and test it between them. Hotch's semen is thick but somewhat watery, a translucent white, estimated six or seven millilitres in volume (which sounds so much more scientific than measuring around an estimated teaspoon). It's actually the sample with the least discernable taste so far; it's a little salty, but rather uninteresting. He knows Hotch's diet isn't particularly exciting, and wonders if there's a correlation.

He manages to get Rossi in the bathroom. It's not an unfamiliar location for Reid to do this, and Rossi doesn't seem to mind where they are. His cock is shorter than average but thick around, and Reid has to concentrate on the task at hand instead of wondering what it would feel like entering him elsewhere. Rossi isn't vocal but he makes sounds, moans and groans and little growls. It's rather endearing of the older man, and Reid is quite thankful that Rossi lasts some time before finally ejaculating in Reid's open mouth. His ejaculate is bright white, there's fair amount of it – more than Hotch – and it's thick, only just on the positive side of unpleasantly so. It tastes salty, musky, a little acrid. He wonders if it has anything to do with Rossi's habit for cigars, and makes a mental reminder to put that in his notes.

He thought Morgan would be the easiest man to convince; he certainly seems like the kind who won't object to a freely offered blowjob. Surprisingly, though, the first time Reid had tries Morgan says he doesn't do things that way. Reid wondered if he was going to have to court Morgan in order to get what he wants, frustrated by how much time that would probably take. However on his second attempt, cornering Morgan in Garcia's empty office, Morgan is much more agreeable. Reid was certainly wrong to consider that Morgan's penchant for a flash car and motorcycle is making up for a sexual lack; his cock is big, and thick. Morgan really makes Reid work hard for what he wants, dirty encouraging words purring out of him as Reid labours – though it's hardly a chore when he enjoys the process so much. When Morgan finally does ejaculate there is a lot of it, enough that Reid swallows before he's finished and makes estimating the volume impossible, and he makes a note he may need to repeat this test. His semen is a pearlescent white, and thick in a way Reid is sure makes it ideal for semen's basic purpose. He's surprised at how sweet it is; sweetness he's read is associated with vegetarian or vegan semen, but he knows Morgan is neither of these. He does know, however, that Morgan is big on eating healthy and loves fruit, so perhaps that has something to do with his ejaculate's sweetness. It's certainly the most pleasant of the three BAU men, though he has enjoys sampling each.

It's two days after the last test that he realises he's lost his notebook. Panic is a little bit of an understatement as he retraces his steps, and when he knocks on Garcia's office it's a last desperate attempt. When she calls him in she's grinning like a Cheshire cat, legs up crossed on her desk, his little black notebook open in hand.

"Well, junior G, this is interesting." She says. He can feel the heat rising in his face.

"I can explain-" he says. He can, but he really doesn't want to.

"I wouldn't." She offers simply, winking at him. "I think I might have some advice for you, though."

"Oh?" he can't seem to form more words than that.

"Use the same sample repeatedly." She turns the page. "Use the same subjects, noting changes in their, er, parameters, and their diets, and see how they correlate. The patterns will be easier to see than all these, ah, 'random samplings'. You can't be sure those aren't a fluke. This way, you'll have some consistency."

"Right." Reid nods. His mouth is very dry, but he can't help smiling at the tech with a newfound appreciation for her existence.

"Also," she adds offhandedly, "if you want another subject, I've got a boyfriend who would do pretty much anything to make his Penny happy. I mean, I'm sure I could give you data, but if you'd rather collect it yourself..."

She holds out his notebook for him, and as he reaches out to take it he can feel her grin mirrored on his own face. Not before now had the idea of a research partner seemed so appealing.