The moment her hand touched the stone, Karyn said "I wish Jon would realize that he actually hates Sarah."
Jon's eyes went wide, then they burned with anger. Karyn was such a bitch! How could she wish something like that?
Karyn waited for the stone to glow, as usual, but nothing happened. Why wasn't her wish granted?
"You bitch!" Jon yelled, kicking Karyn in the gut, causing her to drop the stone. "I was gonna just leave you alone, even after saying all of those horrible things about Sarah. But now ..." He reached down and picked up the stone. Eyes full of hate, Jon decided to put Karyn in her place.
Once again, Jon was about to make a hateful wish, this time towards Karyn. And since this was The Love Stone and not the normal wishing stone, he would fall in love with Karyn after he made his hateful wish.
So then he'd be in love with two people - Sarah and Karyn.
"I wish that you ..." Jon started.
