The stone he put in its place looked almost exactly like Jon's stone, except that it wasn't. It was The Substitution Stone.
It worked just like the normal stone, except that after the wisher states his or her wish, one of the words of the wish is substituted by another word, but a word that would still make some sense.
For example, if Jon said "I wish I was drinking a glass of milk," the stone would then grant it in a number of other random ways, like "I wish Zoe was drinking a glass of milk," or "I wish I was throwing a glass of milk," or "I wish I was drinking a glass of juice." Of course, all of these examples are fairly harmless, but the stone could do a lot worse (like instead of juice, the stone could replace the word "milk" with any kind of liquid, like blood or gasoline or even something disgusting like urine).
