Some Sounds Make Us Cringe, But Why?

I think that most of us can agree that the sound of finger nails on a chalkboard is very unpleasant, but why?

The theories include evolutionary survival mechanisms and the anatomy of the human ear, among others. 

In this interesting video by SciShow, Hank Green explores these theories and talks about the mechanics of the way humans perceive sounds.

Luckily, this video does NOT contain any of the sounds that come to mind when you think of cringe inducing sounds.