Vagina

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

"Unfortunately for you, John, that is also wrong. The sexual organ with the most nerves is the clitoris. Strip and get in your booth, John."

Jack strips, revealing a bit of a gut and a small cock. He doesn't look too happy as he steps into the booth.

"Now, each of your bodies will be modified into the shape requested by the other. Let's turn on the booths!"

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 booths open and you are the first one to step out.