What is it about nails down a blackboard that gives you goosebumps?

the sound, obviously, but why? Is it the frequency or something?What is it about nails down a blackboard that gives you goosebumps?
It's the pitchWhat is it about nails down a blackboard that gives you goosebumps?
It's the horrible sound (shudder) it's too high pitched
my guess is that it affects the nervous system in some way
The blackboard sound doesn't bother me, but I can't touch cotton wool. yeeargh!
Its just the friction between the nail and the board which makes a screeching sound which our ears are not really adapted to as it is at such high pitch.
Maybe...like dogs. Or maybe it was the thought of the teacher doing it.