Aaron Schuster fleshes out the phrase:
While scientific research has refuted Aristotle’s claim that tickling is a uniquely human privilege—not only has tickling been observed in our primate cousins, but scientists have recorded laughter-like ultrasonic chirping in tickled rats [see above]—it has confirmed his intuition regarding the importance of this seemingly marginal and unserious phenomenon. (An additional note on animal tickling: the most famously ticklish beast is no doubt the trout, which falls into a trance-like state when its underbelly is lightly rubbed. This has been known for ages; in Shakespeare’s Twelfth Night, Maria says, while planning to trick Malvolio, “Lie thou there; for here comes the trout that must be caught with tickling.”)
Far from being a meaningless spasm, tickling is intimately bound up with human development and the sense of self. Such is the argument expounded by neuroscientist Robert Provine, who sees in tickling an important form of pre-verbal communication and an element in the creation of the distinction between self and other. A primal, neurologically programmed mode of interaction, tickling creates intimacy through a benign and playful aggression. And the well-known inability to tickle oneself serves an important role in educating the infant about the limits of its own bodily experience, poignantly signaling the difference between self-affection and being affected by the other.
Previous Dish on tickling here.