Tickle is a surprisingly broad and deep problem that has implications for topics ranging from the evolution of laughter and the neurological programming of social behavior to the computation of selfhood in organisms and machines. The starting point of this analysis is that you cannot tickle yourself (the ticklee) - it takes another person (the tickler). Building on this mundane but significant fact, we consider the computation of "self" and "other" and its implications for understanding human behavior and building better robots.