humanity is deffinetly plagued with a fear of the unknown. anything that is out of our normal conception is scary. Another one is being helpless, think about the dentist. People hate the dentist, though there is pain most people can experience more pain during a normal day then they do at the dentist. It\'s the fact that you are the complete mercy of someone else that bothers most people. Another one for the deeply religious people is anything that causes doubt in there beliefe system, a removal of their safety blanket (aka god). I\'ve found this out from my own experience. I\'m writing a novel, in which I eliminate the possibility of a god existing...or at least being what we concieve him as, and I\'ve found that in the proof reading I\'ve had done, the very religious people were set on edge and disturbed by it. While it is a fiction based story, it uses alot of scientific theories that bother people namely horizontal evolution.
So I would say the biggest scary attribute is the removal of peoples safety blanket. Find out what causes people to feel ccomfortable, and remove it.
(if i sound insane, it\'s because it is very, very late, like 5am)