Stunned Students

When they got back to the classroom, so Jon could get his stuff, all the students stared at him. "What?" Steve Johnson walked up to him. "Dude, how did you *do* that?" "Do what?" "Disappear like that." "Oh. Um, that. Well ... um ..." "He's got a magic stone," Sarah said. "Magic?" Steve asked. "Yeah, it grants wishes," Karyn said. "Hey, girls," he whispered to them. "Stop saying all that. I wanted to keep it a secret. Remember?" But it was too late. The whole class heard it. And everyone wanted to make a wish. They yelled out things like "How does it work?" and "How many can you make?" and "Can I wish for *anything*?" What was Jon going to do?