(Tickling is very interesting from an evolutionary standpoint. In effect it is a simulated false threat—someone touching you in a place that is vulnerable [e.g., belly, neck]. This is why tickling only “works” if it is someone you trust doing the tickling—otherwise it is aversive. Nonhuman primates love tickles as much as human infants, and a dog’s joy having a belly rub is probably related to this.)
