As if 2016 couldn’t possibly get weirder, it’s become the year of the terrifying stalker/killer clown. It started in South Carolina as a bizarre marketing ploy, perhaps inspired by Jared Leto’s character in Suicide Squad. But how did clowns — which were invented in the Middle Ages as comic relief and have been a circus staple for generations — go from being funny to frightening?

Steven Schlozman, a psychiatrist who teaches a seminar at Harvard on the neurobiology of horror, explains that our fear of clowns is rooted in a double-take. Our brain isn’t sure what to do when we see a clown: Is it human? Is it not? That question triggers fear, which kicks off that fight-or-flight sense along with a cue to the amygdala to investigate WTF this face is — much like what happens when you’re in a haunted house. A face that’s not quite human, like Pennywise in It or Leatherface in The Texas Chainsaw Massacre might be a sign to back away and run.

“There’s a difference between the kind of scared you get during a horror film and the kind of scared you get when, God forbid, there’s an active shooter,” Schlozman tells Inverse. “And a lot of the science behind that has to do with things like pattern recognition and confirmation bias — essentially, the things that show we’re human.”

This unsettled response is akin to the idea of the “Uncanny Valley” — whether it’s a robot or a Teenage Mutant Ninja Turtle, people get the creeps when something is a humanoid that’s still not quite humanoid. Schlozman brings up the example the “Pale Man” from Pan’s Labyrinth — the terrifying creature whose eyes are on its hands. Humans have evolved to recognizes a face with eyes, nose, and a mouth to be something that is safe. The “Pale Man” isn’t scary because he’s large or because of his sagging skin — it’s because his eyes aren’t where our brain expects them to be.

The “Pale Man.”
The "Pale Man."

And this nonsensical part of faces that aren’t quite human explains not only why some of us aren’t as scared of clowns as others, but also why a certain segment of the population gets a kick out of horror flicks.

“I think one of the reasons why people enjoy the experience is that the brain loves puzzles — we’re wired to love them because it’s a survival mechanism,” says Schlozman. “This happens in our neurobiological gut, in the lower part of the brain way before the cognitive area. People want to figure out what it is about that particular scenario that made them feel scared.”

If the puzzle is figuring out why something is scary, then some of the most helpful clues are the tropes that reoccur in horror films. Studies have found that prior fears ignited from specific cues in scary movies can predict what will scare someone in a different movie. An exaggerated, campy face means a villain; a virginal purist signifies a survivor.

There is a line between “This is fun!”-scary and “I’m going to puke”-scary, Scholzman says, but that differs among people. Some of it comes down to personality; people who measure highly on the Sensation Seeking Scale typically enjoy being frightened more because they have a stronger need to feel powerful emotions. If you have coulrophobia — or a fear of clowns — and stumble upon a clown, let’s just say it’s not going to be a fun time.

But more than horrific faces or weird situations are the things we don’t see, according to Scholzman. “That’s why the original Blair Witch worked so well,” Scholzman explains. “You have a sense that there is always something off-frame, but you never get to see it. On a visceral level, that’s what builds suspense.”

Photos via Giphy, Public Domain Pictures

Sarah is a writer based in Brooklyn. She has previously written for The New Republic, Pacific Standard, and McSweeney's Internet Tendency. She likes cheese especially when paired with a full-bodied joke.