I'm not scared by gruesome or gory. Have you read anything by Richard Laymon? He writes terribly gory scenes. They don't scare me in the slightest. Slashing up people is not scary. You know what's going to happen. It happens. No suspense. No build up. No reason to really care. All his books are like this.
Verdict: Not scary.
Go and visit a real morgue. There are plenty of dead people in there. The people who work there are just fabulous (they have to have a great sense of humor to work there and stay sane I guess!).
Verdict: Still not scary.
I have been dating an Intensive Care Paramedic for 2 years. He sees and describes the worse gore and gruesome accidents/suicides/murders imaginable. Verdict: Not scary. Interesting though
What scares me is the drawn out, deliciously hair-raising, suspenseful lead up to 'something' coming. Call it tension or suspense or foreshadowing or whatever, but when the main character doesn't know what's coming and the build up to showing something bad will eventually happen is what frightens most people. It's when the imagination starts picturing what could happen or what could go wrong that people start picturing the worst without being told.
Verdict: that's scary!
What scares me personally is not always what's going to scare someone else.
Write about what scares you - and then you'll be sleeping with the lights on too!
Lee