Why is the sound of fingernails scraping a chalkboard so Annoying?

[gusl]

Why is the sound of fingernails scraping a chalkboard so Annoying?

I can trigger shivers in my body hair simply by thinking about it.

Comments

[adamas.livejournal.com]

...and yet it's virtually impossible to tickle oneself! :D

[gonzolawyer.livejournal.com]

I get shivers up and down my body from styrofoam. At first it required me to touch the styrofoam. Then it was just being in the same room with styrofoam. Now I'm getting uncomfortable tingles just thinking about it.

And yet I can handle Dunkin Donuts coffee cups. I think that in this case, I made a necessary, life-preserving adaptation :-)