Nails on a blackboard.
There. You don't even have to hear actual nails on a blackboard; you just have to read that sentence, and your neck scrunches back and your eyes begin to shut. Why is that? Researchers in Germany and Austria have just published a study claiming that it's the shape of our inner ear that causes this gut-wrenching reaction. Wired reports that the sounds of "chalk on a slate, styrofoam squeaks, a plate being scraped by a fork," all produce frequencies that actually get louder as they enter our ears. The researchers say they are going to continue their studies trying to remove these frequencies from places like factories and machinery. I, for one, do not want to be used as a guinea pig.