No one - we repeat, no one, likes the sound of fingernails being dragged down a chalkboard... but why? After years of research (yes, they're actually researching this stuff) they've finally figured it out!
A group of researchers from the University of Cologne and the University of Austria believe that the reason behind why we can't stand the noise has a lot to do with the shape of our ears. Specifically, because our ears have evolved to amplify sounds within a certain range of frequencies.
For the scientists to come to this conclusion they had to (you guessed it) get a bunch of very unfortunate volunteers to conduct multiple skin-crawling, nail-scratching experiments on.
50% of the volunteers were told what sounds they were being subjected to while the other 50% thought they were listening to contemporary music.
The study subjects then had to rate how the sounds made them feel and the researchers also took note of their stress responses - by watching their blood pressure, heart rate and perspiration.
What they found is that our ears are extremely sensitive to pitches in the mid-to-low-level range of frequencies. When they researchers removed the sound within this pitch level, the subject automatically rated the sound as more pleasant.
So, there you go... as always, it all falls back to science!