When it glowed, he had an urge to close his eyes. And when he opened them, he panicked. What did that wish do?
When Jon opened his eyes the first thing he noticed was that his body seemed to be below him at the bottom of the stair looking up at him. Then he hear myself yell up the stairs towards him saying, "Damn it Zoe, hurry up and get down here so we can leave. I don't want to spend my day driving you and your Goth friends around. If we hurry I can still spend some time with Karyn."
It was then that Jon realized what his hasty wish had done. He was now Zoe, but what had happened to the real Zoe? And did the Jon down below had the stone.
