Anything that isn't scary by itself isn't that scary.

Any horror fan will tell you that the reason zombies are so horrifying is that while one of them might be easy to avoid, hundreds of them swarming you is overwhelming. This may be true, but how scary is a monster if you need a hundred of them to be frightened? A hundred of ANYTHING is scary. A hundred accountants coming at me is certainly terrifying, but nobody's buying that video game. A hundred raccoons, a hundred school busses, a hundred mannequins, really, you name it, if there are 100 of something, I'm probably going to be scared of it. (Exception: rice.)