A recently discovered system in the brain may help explain why we humans can get so worked up watching other people.

Mirror neurons seem to play a key role in how we relate to each other : the mechanics of empathy. The basic theory is that the brain cannot easily tell the difference between something actually happening to you and the percieving the same action happen to someonelse. It explains why we cry at sad films, how we learn and how we got such a leg up the evolutionary ladder amongst other things...

Watch a PBS film about Mirror Neurons here