"Why? For another silly trick?" yelled Zoe.
"Please, it's not a silly trick!" yelled Jon back. "Let me explain!"
"Fine," said Zoe. She had stopped in her room, and Jon was at the door, but Zoe said "Remember, I still have the stone."
"Don't you get it?" asked Jon. "I wished you couldn't tell when a wish was made on you. Getting nauseous from that wish would make you able to tell. It would be a reversal, and the stone doesn't do that. That's why you didn't get nauseous."
Zoe seemed uncertain, but thought she had something. "I could tell you made the sneeze wish."
"Because you heard it. That must not count."
"So what was I before this? Your non-goth sister? Your brother? Your cousin? Two people? Some stranger? No, you said you didn't want me to tease you. I couldn't have been a stranger."
"Find out for yourself," said Jon. "Wish that I'd have a wish to change you back."
"Oh, fine. I wish Jon has a free wish to change me back."
"I wish Zoe was changed back, cancelling my earlier wish."
And Zoe transformed into....
[Note: this is possible, if Jon made the wish before the "Then Zoe comes in..." chapter, since Zoe never appeared before that. Also, it should be impossible to wish that Zoe can't tell--but the sneeze wish shows that Jon managed to do it somehow even in the main thread.
And Jon's clothes won't change back to a guy's. Even after the first wish goes away, the wish to be a girl would change his clothes all by itself. But it is possible that since he couldn't hear the first wish but could hear the second, he gets his memory back when the first one wears off.]