The stone he put in its place looked almost exactly like Jon's stone, except that it wasn't. It was The Hate Stone.
It worked just like the normal stone, except that after a "friendly" wish is made towards someone, the wisher will suddenly hate the target of that wish ... and then would make additional wishes to harm that person instead of help them, regardless of how they felt about the person before they made the initial "friendly" wish.
The wisher won't think that it's strange that he or she hates the target of the initial "friendly" wish. But everyone else will think that it's strange, whether they heard the wish spoken or not.
