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Source: https://writers.stackexchange.com/a/39360
License name: CC BY-SA 3.0
License URL: https://creativecommons.org/licenses/by-sa/3.0/

Unfortunately while I don't have real science to back me up I am going to try using personal experience and understanding of psychology. There are many types of fear, used in many mediums. The cheapest one is the jump scare. This is trying to trigger someone's fight or flight response. To do this it takes two steps. The first is to put the brain in alarm mode. Make it create as much neurotransmitter as possible to allow the jump-scare. This is kind of like if you look at pictures of flees and suddenly get all itchy. Your brain sees insects to creates neurotransmitters to make itching more likely. In the case of a movie just threatening a jump scare primes the viewer. The thought that something may leap out makes the brain release the chemicals like the picture of the flea. Then you do the actual scare. A rapid change of visual, and auditory. The transmitter is there so neurons easily jump their messages causing an Adrenalin dump. Congratulations you are scared.  
Unfortunately while books can do the first part, they can't achieve the second. You can prime your reader all you want. Tell them something horrible is coming, but you can never startle.

So what can you do? As a writer for that raw cheap fear the best you can do is undermine the feeling of safety. Human beings, like any mammal, create mental safe spaces. This is where we live, and people we know. In these spaces we do not need to make danger checks all the time. We know no one dangerous is in our house. We know our wife is not just going to stab us.  
Undermine these beliefs. Tell the reader that you don't actually for a fact know anything outside of your line of sight. You don't actually know that the person in the other room is your wife, and not a monster wearing her skin. It's not hard. I bet just reading that has made someone's skin crawl. The brain is now going into a higher alert. It is forces to reevaluate it's safety just because it's now processing it. There lies the other fear. Collapse everything the reader knows, and tell them that anything is a threat, and if done at all well it will provide tension for at least a while.

As I have mentioned, both of these are the cheap thrills of horror, not the deep personal horror other answers on this site discuss.

Original score: 2