Trev's machine

Jon didn't at all like the sound of that. "That's like saying 'oops'. What did you do?" "Nothing, except I didn't think it over." Jon thought things looked strange but couldn't quite place it for a moment. "Wait a minute. I think I'm too short. I should be a few inches taller." "Right, Jon," said Trev. "It's just a machine, you know. It can't violate the laws of physics. That's why I had to keep the fat on when becoming a girl, and even then I was fatter as a girl than as a guy. But when you became a girl that must have been real magic. Your mass went down. When I changed you into a guy you kept the same mass, so you're shorter." "Well, I can fix it. I can wish that your machine changes mass. Here we go. I wish that your machine can change mass." A few minutes later Jon was back to normal and they left Trevor's room. "Hi, Trevor," said his mother. "Who's your friend?" Of course changing him back with a machine didn't also change reality back....