Why do people scare themselves and enjoy seeing others scared?

I was playing a horror flash game called “The House”, knowing I was probably going to get freaked out, and did get freaked out. Later, I was with a friend and had him play it. I couldn’t stop laughing at how scared he was getting.

So A) Why do people, despite knowing there will be negative consequences, still play survival-horror game, watch horror films, visit haunted house, etc… and B) Why do people get such a kick out of seeing someone else get scared?

These are both assuming it’s not just me.