The heroine comes into the scenario innocent -- they never believe what's happening at the start of the movie -- but as nubile teens and skeptical black men are hacked to pieces and the story progresses, the heroine slowly comes to understand and accept the situation. She usually learns how to exploit the rules, and in the process beat, or at least escape from, the monster. Long story short: She starts out innocent, but loses it by the end.

From that last sentence alone, you probably already see where this is going. Dang, I already blew my wad. Hey, speaking of ...

Most times, the obligatory panty shot is more clumsily inserted than a junior after prom, but sometimes there's a good excuse for it. In Alien, Ripley strips down to her panties for the climax because she's about to go into stasis. But you can't hyper-sleep in pajama bottoms? Does fleece throw off the chrono-chambers or something? No, that shot, like all horror flick panty shots, is about two things: showing Sigourney Weaver looking awesome in space-underoos, and making an otherwise tough character seem vulnerable.

Cabin In The Woods parodied the trope by kicking it right off with their Kristen Connolly dancing around in panties. In the American remake of The Ring, Naomi Watts finds that pants restrict her journalistic sensibilities, so off they go. In the remake of The Fog, there's ominous banging on the door, and since it's a chilly Pacific Northwest beach night, our heroine does the sensible thing and puts on a warm sweater before stepping outside ...

Just plain forgets the pants, though.

Netflix
"What's that? Cold? Haha, How could I be cold? I have a sweater."

We famously won't shut up about how Alien was chock full of dick symbols and chest rape, and Hellraiser's demons were literal sex beasts. More recently, there was It Follows, which is important because it's a fucking amazing movie, but also because it is a pure, stripped down example of the genre. In the film (spoiler), the horror comes directly from the sex -- the curse is literally transmitted like an STD. And yet Hollywood says my screenplay about a haunted case of crabs, Crustacean Invasion, is in poor taste ...

Why is sex so closely tied to horror? Because sex is a nerve-wracking time; a period of vulnerability where we're without protective clothing, distracted, and -- unless we're Clive Owen (NSFW) or Nicolas Cage (NSFL) -- we can't fight back if something attacks us. We're scared of sex, scared during sex, and scared of not having sex. Horror movies, like pimps and advertisers, are more than happy to exploit sex for their own twisted purposes.

1. Kick her in the crotch

2. Laugh nervously

3. Develop a shameful new fetish

Peter Kramer/Getty Images Entertainment/Getty Images
"Yeah, baby, hangdog it. Uh, yes, do it -- look like a human Eeyore! NGHHH."

Really, the only difference between a good scare and a good laugh is timing. Let's revisit Cabin In The Woods and Scream again, because well-thought-out parody always illustrates what really makes a genre work. Both of the films not only laid out rules for the characters to obey, but hinged on the protagonists breaking them to survive. That's really just meta-commentary on horror in general: Setting up expectations and then defying them.

The Ring had its famous "watch the film, die in seven days" rule. Darkness Falls wasn't the best movie, but it had a good horror ruleset and it never broke them. Pinhead rants about rules in the Hellraiser series almost as often as he pulls nipples off. Or again, watch It Follows (if for no other reason than it is great, and lately it seems like "great horror movie" is a bigger oxymoron than that dude who tried to replace Billy Mays) and you'll see a typical horror ruleset laid out. Within the first few minutes, we have somebody painstakingly explaining to the main character what the monster is, what it does, and how it works. Then the terror comes from trying to manipulate those rules and seeing what you can get away with. Just like doing your taxes.

But once we banish the unknown, the focus shifts from horror to action. Now it's not about fear; the scares come in the setup, while the finale is all about tension. That also explains why, with rare exceptions, the best installment in a horror series is the first film -- well, unless they're planned as a series from the start, like my novel, The Unnoticeables, which is the first book in a planned trilogy! (All right, now I'm starting to enjoy tormenting you with plugs juuuust a little.) After we found out what Jason really was, and how he came to be, there was nowhere left to go but Manhattan, space, and direct to video.

Evil Geeks
Undead monsters can't die ... with dignity.

Of course, any trend has its exceptions: Aliens was fantastic, but better than the first? I don't know. Certainly not scarier. The Hellraiser series did some interesting stuff in the sequels, but that is, in part, because they spread the origin story out. They didn't really answer all the questions until the third film. For the first two, there was still plenty of mystery left -- all we viewers knew was that crazy sex demons come out of a box sometimes.

Hey, I wonder if that sentence contains some kind of symbolism for something. But what? What could a sinful sex box possibly be representing?

A horror movie starts with an innocent who slowly learns all the rules and how to exploit them, but loses that innocence just as the great mystery is explained. Yep: Horror movies are about losing your virginity.

Western culture places a huge amount of importance on losing our virginity. Most of us don't have rite of passage ceremonies anymore. For those of you who aren't fans of having your genitalia mutilated with a rock while bits of it are fed to fire ants, that's probably a relief. But coming-of-age is still a thing we have to deal with. We have our milestones -- getting our license, our first job, graduating high school -- but culturally, adulthood is still tied to sex. Our official passage into this big, scary world is losing our virginity. There's a lot of pressure around it, we don't fully understand how the rules work, and because it's a huge milestone with so much fear and uncertainty associated, it kind of scars us. So we end up telling scary stories about the process to help us deal with it.

Brand X Pictures/Stockbyte/Getty Images
"And some say that penis roams these woods to this very day!"

No theory is bulletproof, of course. That's not the point. I write books. I know what their subtext is supposed to be while I'm writing them, but I've heard fan theories about my own works that make a hell of a lot more sense than my intended meaning. This could be because I'm a terrible writer (buy ... The Unnoticeables?) or it could be because these theories that we come up with aren't meant to tell others how they should be viewing movies, but explaining how we view them, and so giving some insight into ourselves.

That being said, assume what you will about my terrifying and bizarre sex life.

Pre-order The Unnoticeables before launch day, July 7th, 2015, and get a copy of Robert's other book, Rx: A Tale of Electronegativity, for free!. Read more from Brockway at his own monument to narcissism, The Brock Way, or follow him on Twitter.

Be sure to follow us on Facebook and YouTube, where you can catch all our video content such as Why Horror Movie Slashers Are the Best Wingmen Ever and other videos you won't see on the site!

For more from Robert, check out 4 Things You Learn Having a Disease Doctors Can't Diagnose and 5 Amazing TV Shows That Prove Japan Broke Reality.