First off, if you haven't already, check out my publisher's Kickstarter campaign. The $25 dollar pledge gift is a printed, signed copy of one of TM Publishing's titles. My book, The Shifting, is one of them. I'm going to continue to post this message until the campaign is over.
And now, on to today's topic: horror. If you want an entertaining, video overview of the symbolic elements of horror, check out this Extra Creditz video on Youtube. They're talking specifically about using horror in video games, the the storytelling value is still there and this is a pretty good, simple explanation of the self, the uncanny, and the other.
And now for my explanation, more specifically tied to books and movies. Like the video, I'm going to focus on the ideas of the self, the uncanny, and the other. First off: horror is almost always tied to a basic human instinct, particularly the drive to survive. That's why people tend to die in horror stories. The drive to survive is a powerful, emotionally charged instinct, so, when something is tied to this instinct, it becomes a more powerful, emotionally charged form of horror.
The self is, quite simply, the self. This is a reflection of the character or the reader that hasn't been twisted, necessarily. The self includes elements of a person that we are not proud of and try to keep hidden. I think Edgar Allen Poe does a good job of using this in his stories. Think of the narrator of "The Tell-Tale Heart". That guy is nuts. An insane narrator should fall under uncanny (more about that later), but Poe's narrators don't because they make sense. Before the story is over, the reader can see things the narrator's way, and that is creepy to the reader, because Poe is bringing into the light a part of the readers they would rather keep in the dark. in "The Tell-Tale Heart" it's the disgust we feel for people who are different, and perhaps even the desire to cut the disgusting people out of our lives. I can't speak for everyone, but I believe many people may understand how the narrator feels, and because we are horrified by the murder this understandable drive leads to, we become horrified by ourselves.
The uncanny is when things are slightly off. Imagine coming home one day and noticing that all your photos are upside-down in their frames. Or that the radio is playing music backwards. Or that all the food in your refrigerator has gone bad, all at once. There is nothing unduly threatening about any of these situations, but I'm fairly sure that if you encountered one of these situations you'd feel unnerved. Horror films do this a lot to stir up feelings of unease and fear in the audience. One film I think does a good job of using the uncanny is Alfred Hitchcock's The Birds. Birds flock in real life; they fly in large groups. It happens. But when all the birds become slightly off by banding together, regardless of species, and flying in swarms over the town, they become uncanny. Add to that the fear for one's life (the birds attack), and we have horror. The viewer is left with a sense of unease at the end when the uncanny behavior is never explained.
I feel that Ray Bradbury in Something Wicked This Way Comes also does a good job with the uncanny, given his portrayal of carnivals and particularly the carnival freaks. We already think carnival people are uncanny (see the Extra Creditz video for a description of why), and Bradbury adds the element of fear of survival with a sweet, frightening element of the other.
The other is the alien. This is something we do not and cannot understand. Bradbury has a man with hairy palms, a carousel that turns people young or old, and beings that feed on the prolonged pain of fallen souls. We don't have these, we don't understand them, and we don't like what we don't understand. H.P. Lovecraft, from what I've read of his work, does a good job with the other. Cthulhu is terrifying because it is unlike anything we know, and Lovecraft exploits that. He describes the monster as something so awful people are driven mad by it, something that is impossible for the human mind to comprehend. Add the fear for life, and the fact that we never get a good "look" at Cthulhu, and we are in the presence of the other.
One last word: sometimes when writing horror it's better to let the reader imagine. In Jaws, we lose fear of the giant man-eating, uncanny shark the moment we see it. Signs is similar, in that we fear the aliens more before we see them. The mind can create monsters more terrifying than anything set down in words can. With a little room to imagine, the reader will invent something based in the self, the uncanny, or the other, something that resonates with them personally.