Why is the sound of finger-nails scraping across a blackboard so unpleasant?

I think for a couple of reasons: certainly the high frequencies are annoying, but research might say the low frequencies are the more unpleasant. Or the idea we are conditioned to dislike the noise either due to our ancestors or because we've been told to dislike the noise by society -- similar to how being ticklish is learned as well.Why is the sound of finger-nails scraping across a blackboard so unpleasant?
because of the makeup of your fingernails


the rather thin but strong composition. when rubbed against a black board, they do not slide, they sort of jump. this causes several broken high frequency pitches that are audible by the human ear. High pitches stimulate the brain. notice that your microwave, washer, dryer, or other device with a timer use high pitches. this is because these are more attention catching than low pitched sounds. the extremely high pitch of the friction between your fingernails and the blackboard cause your brain to go into to temporary shock. this may cause some people to develop chills or a negative outlook on this sound. people who cant hear these sounds are immune to the effects of the blackboard phenomenon, and should use this to torment everyone around youWhy is the sound of finger-nails scraping across a blackboard so unpleasant?
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The finger- nails rubbing the board creates friction causing the unpleasant sound.
I like the theory that it goes back to our more primitive times when we used warning calls. It caused an instinctive reaction to hide or flee or do something becuase danger was nearby
for some reason it doesnt bother the person whos doin it only the people hearin it
b'coz.......fingers and blachboard dont actually go together