Mrs. Gibson Doesn't Know Karyn

Karyn didn't recognize the young girl, but since she was playing on Jon's lawn, she just figured that it was a relative she didn't know about or the daughter of a friend of the family. She walked past and into the house. She usually entered through the kitchen door, which, as always, was unlocked. "Who are you?!" Jon's mom yelled, so suddenly and loudly that Karyn jumped back. "It's just me," she said. But Jon's mom answered by saying something very peculiar. "And just who are you supposed to be?" "Mrs. Gibson. It's me, Karyn. Jon's friend?" "Who's Jon?" Now Karyn *definitely* knew that something was wrong. Something like this could only have happened because of the stone. What had Jon done?