Being tickled often comes with a whirlwind of emotions: Why are you doing this to me? Why won't you stop? And, why am I laughing about it? Thankfully, this new video from Hank Green and SciShow tells us why we're so gosh darn ticklish — and why tickling creates such a bizarre cocktail of sensations.
As the video explains, we actually use the term "tickling" to describe two different sensations. The first, knismesis, is when we get that urge to scratch after being lightly touched with something like a feather — or, you know, when a bug is crawling on us. Other mammals experience this sensation, too; if a fly lands on a horse, for example, the horse will whip its tail to flick it off.
The other (more fun) kind of tickling is called gargalesis. This is the kind that makes you actually laugh; it's only seen in us primates. When chimps and apes are tickled, for instance, they let out a laugh-like pant. Interestingly, those primates that are ticklish tend to be ticklish in the same few spots, such as at the ribs and under the arms and chin.
Because these are all pretty vulnerable areas of the body, some scientists have speculated that gargalesis is an evolutionary mechanism that functions as a way to teach young apes and humans self-defense. Even though we may instinctively turn away and try to hide those spots from an incoming tickle, we can't help but laugh and, in turn, offer what appears to be an encouraging facial expression. The thinking goes, then, that if tickling didn't make us laugh, our tickler wouldn't feel invited to continue — and we wouldn't learn the vital importance of protecting our tummies. A necessary life lesson, indeed.