Why? I don't know!

The highlight of my day at school is when the bell rings for students to be dismissed at the end of the day. As students are walking down the hallway to their rides, one teacher will pick a student and then growl very loudly at the kid scaring the crap out of them. I find this to be ECSTATICALLY FUNNY to see the kids jump and scream. Why? I don't know. I'm perverted that way. In college every time it snowed, and one year it seemed like it snowed every week for a month, there were some very slick steps across from the lobby of my dorm. I would stand at the window and watch every one fall on those steps. HILARIOUS! Why? I don't know. Then I got married and thought it would be funny to scare my husband when he came home by jumping out of the closet. It was VERY FUNNY! I would roll in the floor laughing. Why? I don't know. That happened about 3 times until he got mad and threw his keys and made a dent in the wall of our apartment. I know I'm not alone in enjoying other people's falling and being scared. I just want to know why? Maybe next week we can trip the kids as they're walking down the hall.