The familiarity of the film's tropes belies the subtly radical spirit of It Follows. Rather than openly mocking and then transcending the genre's conventions, like the fantastic Cabin in the Woods, this film seems to tinker with horror's very DNA. On one level, It Follows seems like a comfortable albeit fresh reshuffling of horror-movie components (sex-as-deadly-sin, a gang of teenage friends teaming up to stop an evil force, scary house chases, a dark-and-stormy night scene). But step back, and it becomes clear just how unorthodox the film is: There are no dream sequences and no hallucinations. No real attempt to unravel the story of "it." No ghosts, no psychotics. Sex means death, but it also can mean life. There's very little gore and few jump scares. It's also got a not-quite-ironic intellectual touch to it: Large chunks of T.S. Eliot's poem The Love Song of J. Alfred Prufrock are recited aloud. And another character—a Hipster Ariel doppelganger, with big glasses, reddish hair, and a seashell Kindle-type device—reads from Fyodor Dostoevsky's The Idiot periodically.

But what's most satisfying about It Follows is how its monster manages to inspire such slow-burn terror when it spends 90 percent of the film doing something decidedly un-scary: walking slowly, often out of frame. Even the absence of the linearly traveling, unrelenting "it" is no relief: The anticipation of its arrival slowly and brutally wears the audience down, like death by a billion spoon thwacks. It's hard to know what to call the thing at the center of It Follows—a spirit? A monster? A villain? Is it even really evil or just a human embodiment of inhuman malevolence? As the director, Mitchell, has said: "There's no logic to it—you can't really explain a nightmare."

The inclination of horror movies to explain and profile the dark force as much as possible often results in a didacticism that doesn't translate well onscreen. Just think of how many films feature a haggard, wide-eyed protagonist poring through old texts, newspaper clippings, or Internet searches, or tracking down old victims in hopes of finding an answer. The process of the investigation itself can be spooky. The little girl was pushed into the well by her mom? Shudder. Rather than cultivating fear in the gradual, deliberate reveal of gruesome details, It Follows' thrust comes instead from training the audience to recoil from the shadowy, blurry figure on the horizon, behind the characters, without fanfare or warning.

The most obvious analogue for "it" is Stephen King's It, which is also a shapeshifting creature. But that monster diverges sharply from the one in It Follows in that it has a famous manifestation (as a very recognizable clown) and plenty of backstory (feeds every 30 years or so, prefers eating children). Even The Conjuring, another recent horror movie widely considered to be a new classic of the genre, dove into the history of the angry spirit that lived in the haunted house. It also spawned a spinoff based on the creepy doll whose face opens the movie: Annabelle. But It Follows does just fine without a famous face at its center.