Scraping a chalkboard (also known as a blackboard) with one's fingernails produces a sound and feeling which most people find extremely irritating.
In response to audio stimuli, the mind's way of interpreting sound can be translated through a regulatory process called the reticular activating system.
The physiological response was a very slight initial fall in heart rate followed by a sharp rise, returning to normal after about 6 seconds.
[2][3] One explanation for the adverse reaction is that the sound is similar to the warning call of a primate, as would have been commonly heard among human ancestors in prehistoric times.
[7] In a 2011 study, musicologists Michael Oehler and Christoph Reuter[8] hypothesize that the unpleasantness of the sound is caused by acoustic resonance due to the shape of the human ear canal which amplifies certain frequencies, especially those in the range of 2000 to 4000 Hz (the median pitches mentioned above); at such a level that the sound would trigger pain in human ears.