Why is scratching on a blackboard so nasty?
Why is it that the sound of someone scratching their fingers down a blackboard makes people wigg out? I personally can't stand the feel of cotton wool rubbed between my fingers. One of my buddies hates the feeling of drying a wooden spoon with a tea towel, and another can't stand the sound of metal spoons on teeth! None of them are physically painful so what is it about these sounds/sensations that gives you that grit-teeth cringe?!
Even imagining these sounds can make your spine tingle. We're not certain exactly why people react to these sounds, but some research has been done by playing these sounds to volunteers (lucky them!). It was found that there is a frequency response to this, so when you play sounds of a certain frequency it elicits the spine-tingling, I-really-cant-stand-that, awful sensation. It's suggested that these frequencies are similar to those produced by an animal that is in distress, so the researchers think that we are tuned to be sensitive to these sounds, so that we pick up on when there might be danger around, and can be primed to react.