Science Class Ruins Your Sex Life

What is happening:
A kiss. A simple delicate, open-mouth, tongue-filled kiss.
What comes to mind while this is happening:
There are more germs in the human mouth than that of a dog's.
Your inner freak-out monologue:
How fucked up is it that I stand a lower risk of making a withdrawal from the Bank Of Communicable Diseases if I frenched the dog instead? Very, that's how. That is the same dog that eats his own shit, just finished his daily 30-minute ball-mangeing ritual, and who I once saw eat a plate of brussels sprouts, gag, throw them back up whole, lick the rug beside the overturned dinner plate to get the taste out of his mouth, walk over to the slimy puke-pile of tiny little cabbages, sniff them, and eat them again. I'm better off kissing that dog's mouth rather than this man's? Blargh.
The mood? It is ruined.

What is happening:
A rollicking (for him, at least) go-round of tuckus lingus.
What comes to mind while this is happening:
There are more strains of bacteria in the typical human mouth than on the typical human anus.
Your inner freak-out monologue:
Yes, but some of those mouth germs taste like mint. And chocolate. Ass germs, I imagine, are severely lacking in the taste department. If they weren't, there would've been organized a long time ago a group of ass-munching gourmets, and within that group, there would've been divisive elitism among those who much preferred the heady taste of musky ass and looked down upon those who indulge in the much ballyhooed 'swamp ass', kind of like the truffle eaters versus the durian eaters in those ridiculous foodie circles. I'm pretty sure the International Brotherhood of Ass-Munching Gourmets (not to be confused with the North American Federation of Assmunches, fondly referred to as "Congress") would offer shitty parasite protection in exchange for monthly dues. As far as ass-eating insurance goes, can you imagine the process of filling out the paperwork? "T'aint or Browneye? (Cirlce one)"...
Where was I? Oh, right. Analingus.
I'll just lean forward and pretend to enjoy it as much as he does.
Note to self: whatever you do, no kissing for the rest of the night.

What is happening:
An energetic foray into doggystyle.
What comes to mind while this is happening:
It is possible to spread HPV just from genital to genital contact without an exchange of fluids.
Your inner freak-out monologue:
Oh dear sweet mother of... was that a testicle I just felt slap against my ass? Fuck! There it is again! Oh, ew. Ew, ew, ew! It's soft and prickly! I'm so confused...! Ack, now it's sticking to my ass cheek. Ew, ball sweat.

What is happening:
You feel the first sensation of fluid exchange as he laps at your pussy. It makes you cringe momentarily. Then you taste the salty precum as you blow him. It, too, makes you cringe.
What comes to mind while this is happening:
Many STDs want to infect warm, wet places, like your mouth, urethra, vulva, vagina, penis, and/or anus. This means that many STDs can be passed from your mouth to genitals and vice versa.
Your inner freak-out monologue:
Do you mind if we take a really hot shower before we get our swerve on? Just a quick, pathogen-killing boil... no big deal. Failing that, would you mind if I swab your meat and potatoes with this sterile betadine solution? It won't sting, I promise. Oh, those gloves? Never mind those. The face mask? Oh, don't you worry. The antiseptic spritz? Oh... erm... lube? What? Why would I lie to you about something like that? Now hold steady while I scrub your cock raw with antibacterial soap.

What is happening:
You feel his erection pulsating under the layer of clothing fabric separating your now flushed bodies.
What comes to mind while this is happening:
"Ithyphallophobia" is a morbid fear of either seeing or thinking about an erect penis.
Your inner cynical monologue:
Wow. That'd be a first.

What is happening:
You're slowling rolling the condom down on his erect member, being careful to both pinch the tip and avoid ensnaring any errant hairs at the base.
What comes to mind while this is happening:
A man will ejaculate approximately 18 quarts of semen, containing half a trillion sperm, in his lifetime. That's 500,000,000,000 little carriers of half his "rampant pussy fiend" DNA.
Your inner logical monologue:
Can we double-bag this?

What is happening:
He grunts and moans as his orgasm sends pulses through your conjoined parts and wracks his body with pleasureful shudders. Meanwhile, you're bored nearly to tears and wondering if you'd hurt his feeling by breaking out your trusty Pocket Rocket.
What comes to mind while this is happening:
Sex is-- biochemically-- no different from eating large quantities of chocolate, in terms of the endorphins produced after the fact.
Your inner monologue:
Pass the Cadbury's.