"I wish" whispered Karyn, "that everyone transformed by Sarah's gun, except Sarah, were to become normal humans of their correct age, and that they'd think the gun just wore off."
Only Jon was close enough to hear her, and he watched as everyone returned to normal. Christy was beginning to grow and become thinner, while her tail retracted to nothingness. Likewise for Tom and Felicia. Then Jon looked at Tiffany Beverly, who was losing the nonhuman hair and extra breasts, transforming back to the girl she was before.
Jon or Karyn might have noticed that Tom was a normal person all right--a normal girl--but they weren't looking directly at Tom and it didn't occur to them at the time that the wish was worded badly.
"I don't know what to do about the teachers," whispered Karyn to Jon. "If Sarah's stone works like yours, we'll have to figure out a way to make the teachers adults without directly contradicting Sarah's earlier wish. I don't even know how she worded it."
"Yeah" whispered Jon back. "This might be hard to do... Wait a minute. Never mind reversing her stone, we can always do that later. We need to get her stone, and do that now! Most of the class saw Sarah make the bitch wish--they know how to use the stone. They could cause a lot of damage... especially if they try to get revenge on Sarah without thinking it through."
Jon walked forwards to where the Sarah-mouse was and bent down to search Sarah's clothing for her stone. He managed to grab the gun, but it was useless--only Sarah could control it, and she couldn't even point it. Meanwhile, someone else's hand grabbed Sarah's stone and Jon stood up only to see a wish being made by....
