Not only does each person find different things scary, but as this article in io9 points out, what scares us as a culture also morphs over time. Here specifically, the author considers why small monsters have replaced larger ones in horror novels and films. It is an interesting point.
From the article:
That's one of the many, many reasons small scares are worse than big ones. Big monsters rely on power, on being extraordinarily huge and vicious. Small creatures are already part of your everyday life. A movie about a big creature has to establish how powerful it is, how it can get from place to place, how it can manage to hide and suddenly pop out of nowhere when you thought you were safe. Small critter movies don't have to do any of that. They just have to rely on what you already know. Small things can already find their way into you safe spaces. Everyone has tried to patch up all the small holes in their house, has tried to seal up their tents, has tried to shake out their clothes and their sheets, only to find the bugs coming back. No one wonders how small creatures get from place to place. They're everywhere. Always. And of course, no one has to wonder how small things hide.Click through to the entire article to read all of the comments too. This article sparked quite a conversation.