Aaron Schuster in Cabinet magazine:
Aristotle famously defined man as the rational animal (zoon echon logon), and as the political animal (zoon politikon). But there are also passages in his work that indicate another less remarked upon, though no less profound, definition. In Parts of Animals, he writes: “When people are tickled, they quickly burst into laughter, and this is because the motion quickly penetrates to this part, and even though it is only gently warmed, still it produces a movement (independently of the will) in the intelligence which is recognizable. The fact that human beings only are susceptible to tickling is due (1) to the fineness of their skin and (2) to their being the only creatures that laugh.”1 Perhaps this notion of the “ticklish animal” was further elaborated in the second book of the Poetics, the lost treatise on comedy; indeed, the relationship between ticklish laughter and comic laughter remains an open question. Should tickling be investigated under the heading of comedy or of touch? Touch, Aristotle argues, is the most primary sense, and human beings are uniquely privileged in possessing the sharpest sense of touch thanks to the delicate nature of their skin. Though other animals have more advanced smell or hearing, “man’s sense of touch … excels that of all other animals in fineness.”2 We might view tickling as a side effect of the hyper-sensitivity of human touch. Our peculiar vulnerability to tickling is the price to be paid for more sophisticated and discriminating access to the world.
Why do people laugh when tickled? Why can’t you tickle yourself? Why are certain parts of the body more ticklish than others? Why do some people enjoy tickling and others not? And what is tickling, after all? In fact, it is not so easy to pin down the phenomenon, as a number of scientific studies attest. Here’s one attempt at a precise description: “Tickle may thus be finally defined as an intensely vivid complex of unsteady, ill-localized and ill-analyzed sensation, with attention distributed over the immediate sensory contents and the concomitant sensations reflexly evoked.”