Genevieve, USA asked:
Why does the sound of nails on a chalk board get such a physical reaction from us?
Itís horrible, isnít it? The reason for this is not 100% known but there is a hypothesis. The idea is that the kind of frequencies that you get when you get the fingernails-down-the-blackboard experience is similar to the kind of frequencies that animals release when theyíre in distress. Itís a kind of distress signal and therefore we are pre-programmed or galvanised into action by those particular choice of frequencies.