"I wish this tack wasn't here until I put it back here!"
The tack instantly vanished, probably to reappear on his desk or somewhere, if he bothered looking for it. And Jon instantly stopped hurting, because when a wish does something it changes reality and if the tack was never there Jon would never have been be hurt.
But wait. The stone was changed; couldn't that cause problems? Jon thought it over and figured it out. At least he thought he did.
There's more than one kind of reversal clause. If it said "you can reverse this by picking the tack off the desk and putting it back on the floor", that's harmless. If it said "you can reverse by clapping your hands and having the magic wear off", that alters reality, so not only would the tack be on the floor again, he'd also have a sore foot.
Unless it was something he really would need to reverse, the first kind is usually better.
There was a solution, though. Deliberately add a reversal clause to the wish. If he says "I wish I'm at school but can leave school by walking", he prevents the stone from deciding that instead he leaves school as soon as he claps his hands.
"What?" asked Karyn.
"A future version of me. Replaced the stone. She was a girl and I think she didn't want me to make the mistake that turned her into one. So now every time I make a wish it makes me add a way to reverse it."
"Too bad it didn't do that for my hair and breasts. Maybe it would have made me say that I can get rid of them by removing them."
"Hmm. I think that'd work. I think it might even work now. I just have to wish that they're fake. "I wish that Karyn's new hair and breasts are a wig and fakes over her normal hair and breasts and that when they are taken off and put back on they become real again."
Karyn held a hand to her chest. "I can feel it! They're gone..." She then reached under her shirt, and pulled out two breast-shaped pads with sticky tape on the back. She tossed them to the side and followed with her wig.
Which should be fine. What are the chances that someone would accidentally put on a pair of fake breasts and have them turn real, after all?
