为什么指甲上粉笔薄熙来的声音ard get such a physical reaction from us?

It's horrible, isn't 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 they're in distress. It's a kind of distress signal and therefore we are pre-programmed or galvanised into action by those particular choice of frequencies.