It’s that time of year when spooky is in season, which means haunted houses, ghoulish costumes, and, of course, horror movies. One particular offering from this year’s crop had us super-freaked out: Annabelle, the new flick about a doll possessed by a demon that comes to threaten a young couple. There’s something about that eerie porcelain face that straight-up gave us the heebie-jeebies.

Of course, Annabelle is far from the only horror movie to focus on the potential creepiness of dolls. There’s the alway terrifying Chucky from the Child’s Play series, and campy B-movies like Devil Doll and Doll’s Playground. So what is this such a thing? We did a deep-dive into what makes a doll scary so you don’t ever have to wonder why you’re freaking out again.

First of all, fearing dolls is a fairly common condition. It even has a name: Pediophobia. (And don’t be too embarrassed if you have it. Channing Tatum totally does too.) So what is it about dolls that’s so creeptastic?

Pediophobia is part of a larger category of phobias about figures that look like but are not human. It has a long history, too. Sigmund Freud theorized that the condition came from a childhood fear of inanimate objects coming to life. There’s an uncertainty about lifelike things being alive or not, essentially, and since dolls are often made to look like children, it can trigger that fear response.

But the other explanation is a neat phrase called “the uncanny valley.” It’s a theory first developed in the 1970s by Japanese roboticist Masahiro Mori, and the idea is basically this: Things that attempt to look like humans almost but don’t quite resemble them, it inspires a feeling of revulsion in people. Mori observes that with robots, the more they resemble human qualities, the more users like them and operate them, up to a point. But when the robots became too lifelike, the users experienced feelings of fear and hatred. Past that point, we can’t tell that they’re artificial.

Dolls, for some people, fall into the space in the uncanny valley that makes them unbelievably creepy: Too humanlike to be an inanimate object. (It’s also a principle that animators use for movies, attempting to make characters human enough to be relatable but not so person-like as to fall into that category.) So stuffed animals are cute, but porcelain dolls can be menacing and creepy. That’s why dolls like the ones in Annabelle have become such a trope in horror movies: They tap into that fear we have of things that are attempting to be but are not human.

“As inanimate objects, they are just scary,” Annabelle director John Leonetti told the Huffington Post this week. “If you think about them, most dolls are emulating a human figure. But they’re missing one big thing, which is emotion. So they’re shells. It’s a natural psychological and justifiable vehicle for demons to take it over. If you look at a doll in its eyes, it just stares. That’s creepy. They’re hollow inside. That space needs to be filled.” Leonetti says.

He actually changed Annabelle’s eyes, after the original doll-maker created her, to make them even more demonic. “I changed her eyes slowly and dirtied her up,” he said. “I had demon eyes made that just makes everybody go, ‘Uh-oh.'”

Meanwhile, artist Lisa Scheffer, who specializes in photographing and painting scary dolls, points to some other dividing lines that make a doll go from cute to creepy—for example, aging, peeling doll skin, or a wandering doll eye. She told about one doll she found at an antique shop.

“It didn’t look too creepy to me,” she said, “and I was on the fence until the guy selling it pointed out that ‘come on, she’s got yellow eyes and things missing.’”

Yeah, that’s pretty scary. Moral of the story? Not all dolls are creepy. Just the old, porcelain-faced, deteriorating dolls with eyes that look like they could be inhabited by demons. You’re welcome.