The computer says "Tammy"

"Yes! My turn! My turn!" Yells Tammy. Samantha lets out a quiet harrumph. Tammy throws the tape measure to one side and launches herself at you. She clasps your face with both hands and parts your lips with her tongue. Her hot breath mingles with your own. Desperately she kisses you. After a long, long time she pulls back slightly. Her cheeks are burning red. She looks away.

"This is all part of the experiment! ... I'm - uh - testing the pH levels of your saliva... With my tongue..."

You wrap your arms around her and hold her tight. She smiles and nuzzles your neck. Slowly you guide her hands to your ass. Reaching down, you palm her rising erection beneath her skirt. It pulses under your grip. Her hands start to knead your bare butt cheeks.

Your stomach rumbles. A dull pain.

"It's happening again," you murmur.

"Let me help you," she pants.

"Just be gentle, okay? This is new to me, and we'll have all week..."

Tammy gulps. "I know... I promise I'll take it slow. It's not every day a guy like you spreads his legs for me... I can be — really awkward sometimes..."

You assure her she's doing fine. Tammy takes off her skirt and panties. Part of you hates to admit it, but when you see the beads of pre-cum forming at the tip of her cock, you feel a craving in your core. Your butt hole twitches in anticipation. When she presses it against your rosebud, you open your mouth to ask for lube, but with a small push she slips inside of you.

"It's like you're pulling me in," she groans.

Samantha eyes you curiously. "Don't you feel any pain?" You shake your head.

"That is unexpected." She makes some notes.

Then Tammy starts to thrust. Your head is foggy, and if Tammy's face is any indication, hers is too. Her mouth is open, tongue hanging out. Her eyes are unfocused but her hands grip your thighs like a vice. She needs this, and so do you. She hits something inside you and you moan without meaning to. Samantha, off to the side, is scribbling frantically, one hand on her stylus, the other jerking her cock.

You can feel Tammy's pre-cum moistening your insides. But just as you feel it, it seems to disappear.

"How are you - flexing your muscles like that?" Tammy gasps.

You tell her you're not doing anything.

"It's the change," groans Samantha. "His body is absorbing everything you can give him. He needs more. He's literally made to take girlcock now." A bolt of white erupts from her cock and splatters against the side of the lab table. You can smell it. Your mouth starts to water. You beg Tammy to fuck you harder. You don't care how you sound, your whole being is crying out for more.

Tammy obliges - she leans forward and forces you down onto the table. Her breasts push against your chest and her breath is hot against your skin. From behind she pumps into you mercilessly. Her hips slam into you with animalistic vigor. You never want it to end. Is this your life now? Maybe that isn't so bad... A heat overtakes you. Everything feels warm and fuzzy.

Then you feel it. Tammy's cock spasms. She cums. Jet after jet explodes into you. Each burst of cum is accompanied by another slam of Tammy's cock. Why does it keep going? Two spurts, three... Your hungry gut fills with her seed. Still there's more. You feel her cum welling up inside of you. Later on, you'll wonder how you never noticed your belly expanding to the size of a watermelon. But for now, you're too distracted to know, or to care.

Samantha has recovered from her earlier ejaculation and is back to note-taking. "I've seen you fuck a guy before, Tammy, and you've never lasted this long... Could he be changing your body too? Or are you simply reacting to him? This will require ... further investigation."

You can only hope.