At last, the mystery has been solved of why the sound of long, sharp fingernails running slooooowly down a dry blackboard can induce chills and screams just by description alone. And we can all thank a group of scientists from Germany, who subjected a number of participants to that very sound over and over and OVER and OVER and HAHAHAHAHA!!!

Half the people were told the sound was part of an avant-gare musical piece; the other half was told that they were being tortured in precisely the way that they were being tortured. All vitals were then measured and they were asked to describe how the sound made them feel.

The ones who thought they were listening to music found it slightly less unpleasant, yes. But both groups found it pretty fucking unbearable, and that's because the sound's pitch falls somewhere between 2,000 and 4,000 hertz. That's a perfect sweet-spot for humans, as the sound tends to get amplified inside the ear canal. The new theory discounts a crazy older one which suggested that the sound mimics primate warning calls. They'll present their findings at the Acoustical Society of America annual meeting in San Diego this week.

Thanks, German scientists! Now break the Knuckle-Cracking Code, the Eyeball-Touching Effect, and Random Mayonnaise Revulsion Syndrome. We need answers! [ABC News, Image via Shutterstock