Rachel closed her eyes and waited a moment for Mark to pick the chocolate. Then she felt it slipped into her mouth, and though she tried to identify it's shape, it melted too fast. Her body tingled all over, but she couldn't tell what part of her was changing. The chocolate tasted good, though, and Mark fed her at least four pieces.
Finally, Mark told her she could open her eyes, and as she did so she felt him place his hand on her crotch - where her vagina used to be. Now there was just a blank patch of skin, devoid even of pubic hair.
"You did mine, I did yours." Mark said, grinning.
Rachel grinned back; she had just had a great idea. Picking up a few dark chocolates, she proffered them to Mark. He took them and saw that she had picked out a dark chocolate pair of breasts and vagina.
Mark looked up at her and saw she was already popping a dark chocolate penis in her mouth. "Let's get it on," he said, and gobbled the chocolates down.
It was odd, growing a pair of breasts; they were delightfully sensitive, but heavier than he thought they might be, and bulkier. His vagina he barely noticed at all, though when he put his finger between his legs a sensual shock wave rippled through his body. Meanwhile, Rachel was glorying in her expanding penis, which was far larger than anything Mark had ever had, to his distress.
Rachel looked up at Mark for a moment. "ooooh," she cooed, and then lept on him.