Why does the sound of nails on a blackboard elicit a physical response?

Chris - It's making me cringe just thinking about it. This is quite a commonly asked question. The answer is psychologists and scientists don't know for sure. One very plausible theory is that when you run fingers down blackboards the frequencies you hear are very high-pitched and the high-pitched frequencies are very similar to the frequencies that animals produce when they're in distress. On argument is that we are genetically programmed and tuned-in to be sensitive to those frequencies. That may alert us that an animal of our own species, perhaps, is in distress. Perhaps it's being attacked or eaten or is in danger. Therefore, by galvanising your attention and waking up and paying attention to that noise you're therefore on high alert and you can make plans to run away or fight. That's probably the best explanation there is for that at the moment. Helen - I like the idea of experimentation on other animals to see which ones are sensitive to nails on blackboards. We can put them in rooms perhaps and see which ones jump the most when we scratch our nails.