Why are people afraid of things that they know are harmless or non-existent? For example: Why do horror films/stories leave people scared after they have finished? Someone may see a harmless spider somewhere that isn't even on their property, and still be scared of it. What is the phenomenon behind this?
closed as too broad by Why Do You Think That Is True, Community♦, Krysta, Josh Gitlin♦ Aug 30 '13 at 21:10
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