Or more precisely, with Jon's father oblivious, since Art heard his/her own wish and would surely know what just happened.
At any rate, Jon, looking around for his magic rock, had been looking out the window, and he saw something get thrown out of another window. It was the rock! It landed right by... a bunch of other rocks.
Jon quickly ran to the door, opened it, and raced outside to pick up the rock. If he hadn't noticed exactly where it had landed, he could have had a hard time finding it. Even then, it took him ten minutes looking through rocks before he was sure he had the right one.
"I wish that my first wish happened the way I meant it, so Mom and Dad get along but Art's back at his home and isn't combined with Mom."
Since the stone let wishes be reinterpreted, he could reinterpret the wish to happen the way he wanted. He had to look away, though there wasn't anything in front of him to look away from, and when he entered the house again, he saw his mother and father, looking like normal again.
Of course, Jon had never heard the penis and balls wish, and certainly hadn't reversed it... so even though his mom and Art were separate, the wish was still in effect....
