Most people associate this cringe-worthy noise with words like "piercing" and "shrilling." But it isn't actually the sound's high-pitched tones that give us goose bumps. During a study that dates back to 1986 (the days when they actually used chalkboards), scientists at Northwestern University tested this theory by removing different frequencies from recordings of nails scratching a chalkboard. These scientists, Randolph Blake, D. Lynn Halpern and James Hillenbrand, asked subjects to rate a series of individual sounds based on unpleasantness. They found that eliminating the highest frequencies from recordings did not improve unpleasantness. Instead, when they removed frequencies from the middle or low spectrum of the sound, subjects gave more positive ratings than when all of the frequencies remained.