Why are accidents so much fun to watch?

Sad and sadistic, yes, but bloody true. If a batsman is wincing in pain when a fast bowler hurts him where it hurts most, we laugh. When we sit down to watch Formula-1 races, there are some who send up a secret prayer for a nice little crash. And then this, the crash of the century. So far.

What is it about sporting accidents that makes it so much fun to watch?