This is a passage from V. S. Ramachandran's book The Tell-Tale brain which is an exploration of the abnormalities in human brain function and what they can reveal about how the brain works. Its super interesting and looks at all kinds of weird and unusual phenomena such as synesthesia (seeing numbers as colours, tasting words etc) and phantom limbs.
This passage really fascinated me though- its an explination of humour, why we find things funny- in scientific but simple terms.
Any joke or humorous incident has the following form. You narrate a story step-by-step, leading your listener along a garden path of expectation, and then you introduce an unexpected twist, a punch line, the comprehension of which requires a complete reinterpretation of the preceding events. But that’s not enough: No scientist whose theoretical edifice is demolished by a single ugly fact entailing a complete overhaul is likely to find it amusing. (Believe me, I’ve tried!) Deflation of expectation is necessary but not sufficient. The extra key ingredient is that the new interpretation must be inconsequential. Let me illustrate. The dean of the medical school starts walking along a path, but before reaching his destination he slips on a banana peel and falls. If his skull is fractured and blood starts gushing out, you rush to his aid and call the ambulance. You don’t laugh. But if he gets up unhurt, wiping the banana off his expensive trousers, you break out into a fit of laughter. It’s called slapstick. The key difference is that in the first case, there is a true alarm requiring urgent attention. In the second case it’s a false alarm, and by laughing you inform your kin in the vicinity not to waste their resources rushing to his aid. It is nature’s “all’s okay” signal. What is left unexplained is the slight schadenfreude aspect to the whole thing.
And the same holds for tickling. The huge adult approaches the child menacingly. She is clearly outmatched, prey, completely at the mercy of a hulking Grendel. Some instinctive part of her—her inner primate, primed to flee from the terrors of eagles and jaguars and pythons (oh my!)—cannot help but interpret the situation this way. But then the monster turns out be gentle. It deflates her expectation of danger. What might have been fangs and claws digging fatally into her ribs turn out to be nothing but firmly undulating fingers. And the child laughs. It may well be that tickling evolved as a early playful rehearsal for adult humor.