There aren't really a lot of scary movies out there. Sure, there's aisle upon aisle of "horror" movies at your video store, but that's where the fine line comes in. The standards for what makes a horror movie are basically things like multiple murders by masked or deformed men, monstrous creatures from other worlds or scientific experiments gone wrong, paranormal hauntings, that sort of thing. Most of the time, people are dying for some reason. The only problem is, the masked men are usually unmasked by the end and either die or supposedly die and then come back, the origins of the monsters are explained and their complete appearance revealed to be ultimately not that big a deal (beforehand you just see flashes of glowing eyes, bloody teeth, and/or slimy body parts), and the hauntings are either not paranormal or just explained and eliminated.

Therein lies one of the 3 big problems. You have to ask yourself, "What scares humans the most?".
The answer you'll usually get is, "What they don't understand.".
There you go, we've identified one of the biggest problems with these movies; the scare is explained. What happens then? Usually, you're not scared anymore. How do you fix this problem? Don't explain the scare tactic. If it's a perfectly normal human being (except maybe in the mind), there's not much you can do until you get down to their reasons.

Another problem is, the scare is usually stopped in the end. There may be various, failed attempts throughout the movie, but it's over by the end. The masked man is caught and/or killed, the monster is killed, all the questions are answered.

Then, of course, there's the motive. The masked man is exacting a revenge on specific people or specific types of people, the monsters are predatorial or just hungry, the ghosts want people out of their homes. You can usually mix this in with the scare being stopped.

So, how do we make a scary movie? It's as simple as taking the answers from above, and doing a 180. If the scare isn't flat-out human, don't explain what it is. Unfortunately, there aren't many scare tactics you can run with without seeing what's scaring you. You have to see the human, even if he is masked. You have to see the monster, even though if you have the best animatronics and/or computer rendering there is, the monster will almost always seem buffoonish.

Whatever it is, it can't be stopped. Humans that can't be stopped are usually the masked men that either only allegedly died and then come back, or guys like Jason Voorhees, who seem immortal. The problem is, these fiends only express their cheap unstoppability through multiple sequels. It's much scarier to try and do it all in one movie. Scary ghost movies usually occur in haunted houses, or possession- based movies. If you can't exorcise the problem from house and home, you can either run away from the house (leaving the ghosts still unstopped), or the ghosts will either trap you or follow you wherever you go. The scariest use of this device comes with applying it to monsters. Sure, you can just blow up the genetically engineered super- bear, or electrocute the little space goblins all at once. What about an uncurable virus? A monster that multiplies or gets worse the more you try to destroy it?

Why are people dying? To make it scary, you basically have to go nuts and ask, "Who cares?!". Jason Voorhees and Freddy Kruger kill only teens. Son of Sam kills only long-haired brunettes. What's the problem with that? Adults and short-haired blondes aren't scared of being killed. Most monsters kill for no reason, but once you see them, you're not scared.

Humans are scared of the unknown. They don't want to deal with what they don't understand. If you don't want to deal with it, you don't want to be in the movie. If you're too scared to even watch the movie, you don't want to be in the movie. If you don't want to be in the movie, then you wouldn't want to be in the situation that the people in the movie are in. You don't want to have to board your doors and windows up to keep zombies out. You don't want to leave the planet to avoid an airborne disease. You don't want to wake up with friends and family seeming like totally different people. Scary movies that cause you to feel this way usually have an unstoppable force that grows in strength, and DO NOT HAVE A HAPPY ENDING. If you don't feel safe throughout the movie, what's scarier than a complete lack of the proverbial "knight in shining armor"? If you're not happy in the first place, and you're not happy at the point when you think you should be happy, what chances do you have of EVER being happy?

Here's some movies that do a good job of keeping you up at night, and looking over your shoulder at every turn, in no particular order of fear-factor or favortism:

You get the idea of what happens next : hundreds of zombies (with wicked makeup, especially the "tar-man" and the legless zombie) running around screaming, determined to (I know this sounds lame, but) eat your brains. There is a reason for this, but that doesn't save anybody, especially when the final solution doesn't work in the long run. All in all, the zombies can't be killed, are very smart and flexible, and burning them's a bad idea. These are zombies at their best. These are zombies meant to scare the shit out of you, and they do. I dare you to sit in the driver's seat of an ambulance, have the passenger door swing open, have a screaming zombie literally lunge at you, and not be scared. Many fansites on the net will tell you this is a comedy- horror movie. This is wrong; there are a couple of humorous sight-gags and lines (the pinned-down butterflies moving their wings, zombies using ambulance and cop-car CB-radios to request more cops and paramedics), but they don't quite add up enough to constitute even a half-comedy. This isn't just a night of the living dead... it's an environment for a never-ending nightmare.

Pretty short list, eh? Well, I haven't seen every horror movie there is, but there's plenty that look too ridiculous to be scary. Don't worry, though, there's some movies that have the right stuff, even if not from start to finish: