Clitoris

"I believe it's the clitoris." John answers.

"And that is the correct answer! Now, Doe, please step into your booth for two levels of programming! The first will change your body into John's perfect fantasy type; the second will make your throat, ass, and pussy extremely flexible, so you can be stuffed as much as he wants, but never lose that virgin tightness. Please step into your booth."

Your booth is actually filled with a kind of gel that reminds you of shoe inserts. It's blue and about the same density, conforming to your body. You hear the hum as the booth turns on, and the gel begins to melt slightly, clinging closer to your body. Suddenly long, thin tendrils of it snake into your ass and pussy. At first it's uncomfortable, but soon it feels extremely good. You moan softly as a current runs through you, and in seconds you are humping the thin tendril of gel for all your worth. You explode as you climax, breathing so hard it take you a minute to realize the machine has died down. The booth opens and you step out.