To me, there's a huge difference between being started and horrified. Plenty of movies have startling moments, but that alone doesn't qualify it as a Horror flick for me.
It takes quite a lot for a true horror movie to impress me. Blood and guts won't do it. If it's too fictional (Nightmare on Elm Street, the Jason flicks, Chainsaw Massacre (any of them), Saw...) it doesn't impress me. The more true to life it is, or the more it rings true to real life sick human psyche's, the more it scares me.
IMHO, "The Boy in the Striped Pajamas" is the most horrifying film I've seen lately. THAT movie gave me nightmares, because it COULD have actually happened (even though it didn't).
The trick for me is, don't try to make fake look real. Take what IS real, and write me a story out of that. That is true horror.
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I'm not likely to be around much longer. As before when I first signed up here years ago, I'm finding that after a long hiatus, and after only a few days back on here, I'm spending way too much time here again already. So I'm requesting my account be locked, banned or whatever. It's just time. Until then, well, I dunno...