You know the scene well. A girl is running for a life, charging across a field, or through the woods, a crazed killer chasing her, and at the worst possible moment she falls down! You scream at the screen, mocking her for her clumsiness. So why is it that slasher movie victims continue to fall down?
In order for slasher movies to work, the genre tends to take liberties. Killers are omnipresent and the victims are useless. We're supposed to root for the killer, particularly with modern horror, where the kill scenes are often what people root for, but still, people should not fall down as much. In Texas Chainsaw 3D, lead character Heather is constantly tumbling over herself, laughably so, and with audiences so aware to this cliche, why does it still exist.
My answer? Because without it, the slasher movie wouldn't work as well. Imagine it - all the supposed victims are athletic and capable. The killer would never catch them, and that would be boring! In addition, we're supposed to feel the sheer terror the person being chased feels. They are supposed to be at least a little vulnerable. How can there be tension if the supposed victim is clear of the killer within seconds every time? Answer? Make them fall down!
Films like Scream, and more recently, You're Next and Cabin In The Woods, have played with the cliches, and turned things on their heads, but at the end of the day, people watch slasher movies to see teens getting slayed in ever more creative ways.
So next time you see a girl fall over, only to be caught by the killer and butchered, rejoice instead of frowning. You're in for a much more fun ride!