Sitting on the toilet was Zoe, Jon's not-very-little sister.
Since Zoe hadn't heard the wish, she remembered them as having already been in the bathroom. Unfortunately, while she didn't know they teleported in, she remembered them as having been in the bathroom because she accidentally left the door unlocked and they just barged in--which wasn't much better.
Zoe did the first thing which came to mind. This was, of course, to scream her lungs out.
Jon reflexively grabbed Karyn and quietly said, "I wish we were in Karyn's room."
Of course, nothing happened, since this would have reversed the wish that they be in the bathroom, and wishes can't be reversed.
