A few houses down from Jon's, a man was about to have sex with his wife. They had only been married for a year and they had been trying for some children.
Before David (the husband) put his penis into Marilyn (his wife), it tingled. He looked down and it was gone! His penis was gone!
Jon was in the bathroom still, but he was not himself. He had turned into David's penis and as a penis, he was laying on the bathroom floor.
Sex organs don't have brains, by the way, so when Jon changed, his mind ceased to exist. It would be back, however, in a month, when he changed back to himself. But until then, he'd just be a sex organ.