Ali Cook

This is fascinating, but it's going to be unpleasant for a moment – just to warn you. Ready?

Imagine the sound of fingernails scraping down a blackboard.

Sorry, sorry to do that to you. But apparently science has worked out why it makes us cringe. The frequency of the sound is really close to the sound of a crying baby, or a screaming adult. The immediate visceral response we feel might have a survival purpose – save the child!

Scientists in that study found that the sounds changed listeners' skin conductivity – i.e showing there's a measureable, physical stress response in the body when we hear these horrible noises. If the volunteers had been told the sound came from an edgy new musical score they rated it less unpleasant, but their skin still 'crawled' according to the scientific instruments!

Researchers found the warning cry of a chimp is similar to the sound of fingernails on a chalkboard, too. So it's possible we're sensitive to sounds like this because they're a kind of primitive warning sound.