As with so many other complex human behaviours, our animal cousins can help us understand what tickling is all about.
There are two types of tickling, and they both have great names: knismesis and gargalesis.
Knismesis is a primitive response, a slightly irritating sensation triggered by a light movement across the skin, and it is widespread. “I would think that lizards, insects and virtually all beings have some sort of behaviour that has to do with defence of the body’s surface,” says Provine. Animals need to defend their bodies against biting insects and parasites, whether that means a quick scratch or a flicked ear, and knismesis describes such a response.
Gargalesis, on the other hand, is a singularly mammalian phenomenon. It is a harder tickle that results in laughter and is linked with play – a distinguishing feature of mammals.
At a basic level, tickle is a sensation involving nerve fibres associated with both touch and pain. But there is more to it than that. “Laughter-associated tickle might best be considered a social behaviour rather than a reflex,” writes dermatologist Samuel T Selden in a 2004 review of the subject. Somewhere in evolutionary history, tickling became funny.
tickle: vt. 使发痒；使高兴// n. 痒感
primitive: adj. 原始的, 早期的
irritating: adj. 气人的
parasite: n. 寄生虫
flicked: adj. 轻打的
reflex: n. 反应能力；反射作用
dermatologist: n. 皮肤病学家