Asked by: Joseph Hill, London
It has been hypothesised that it evokes the sound of babies crying, but it's really not so much the sound itself as the thought of scratching our own nails down a blackboard.
This is quite a painful thing to do because the vibrations are transmitted directly to the nail-bed and we may just be empathising with that sensation.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.