After feeding time was over, Zoe put Jon in his crib. The stone was probably on the floor somewhere, so he wouldn't have a chance to get at it. That is, if he could even grab it at all. His body just wasn't as maneuverable as it used to be. He needed to get back to normal!
As Zoe was leaving the room, she accidentally stepped on something. Jon looked and saw what it was. It was the stone!
"How did this get in here?" she asked. Then she left the room, taking it with her.