These days, horror movies are easy to identify: If it has one or two gratuitous disembowelings, a few naked breasts and leaves us feeling more nauseated than scared, it is, by definition, a horror flick. At one time, though, the cinematic definition of horror was broader. Not long ago, for a film to be labeled “horror,” it actually had to be horrifying — meaning, it made you stay up all night by instilling within you a fear of some kind of vague threat, not by making you have to vomit every few minutes. In honor of the true spirit of Halloween, here is a not-at-all-exhaustive list of gems that may not be listed under “Horror” on Netflix or in Blockbuster (do they still have those?), but will scare the bejesus out of you nonetheless.

Un Chien Andalou (1929)

If you hate the mindless gore-fetishism of the Saw and Hostel franchises, blame Luis Buñuel and Salvador Dalí. Fifty-three years before Eli Roth even emerged from his mother’s womb, the legendary director and painter — the 20th century’s original art terrorists — laid the groundwork for “torture porn” of the new millennium in the opening sequence of their 16-minute short film, the brilliantly nonsensical Un Chien Andalou: a man, played by Buñuel, pries a woman’s eyelid open and, in an unwavering close-up, slits the pupil with a razor. Things, naturally, are uphill from there, if only by comparison, because after you’ve seen the contents of a woman’s eyeball (it actually belongs to a dead horse) spill from its socket, rotting donkeys on top of a piano and ants crawling from a hole in human hand aren’t as shocking as they would be otherwise.

Persona (1966)

For men, the fact that women, if kept in close proximity for an extended period of time, can actually synchronize their menstrual cycles is an unbelievably terrifying notion. Ingmar Bergman takes that bone-chilling concept a step further: What if two women, confined to an isolated seaside cabin for weeks, eventually became the same person? Persona is the recently departed Swedish auteur’s surrealist masterpiece, and critics still argue over its meaning. But an understanding of psychoanalysis and the Brechtian technique is not required to be deeply creeped out by it. Bergman rattles nerves right from the beginning with a seemingly unrelated montage of random, wacked-out images, including a spider, a dead lamb, a crucifixion and — was that an erect penis I just saw? There are several meta-filmic references included to remind us that what we’re watching is just a movie, but they do nothing to diminish the ethereal trauma of the whole experience.

Straw Dogs (1971)

In his prime (read: when he was alive), Sam Peckinpah had a reputation as America’s supreme orchestrator of onscreen violence — his nickname was Bloody Sam, after all — but even his bloodiest films were tempered by an tinge of gallows humor. Not so with Straw Dogs. While not as unremittingly brutal as, say, The Wild Bunch or Bring Me the Head of Alfredo Garcia, the first third of the movie carries a sense of unease that burrows beneath the skin and builds and builds until, inevitably, someone gets a bear trap clamped on their head. Starring Dustin Hoffman as a mild-mannered mathematician who tries (and fails) to escape the turbulence of city life by moving his wife to a quiet town in the English countryside, it remains a controversial piece of work, particularly due to a rape scene in which the female victim appears to be enjoying the violation. What’s truly unsettling about the film, however, is its underlying message: that no matter where we go on this earth, no matter how hard we try to live peacefully, violence will find us. And as much as we like to think of ourselves as pacifists, deep down, we are all capable of carnage. Hey, what’d you expect from a guy known as Bloody Sam? Incense and peppermints?

Return To Oz (1985)

In the 1980s, kids movies took a turn for the disturbing. At the midpoint of the decade, Hollywood released a rash of live-action fantasy adventure flicks, each apparently intended to scar the childhoods of its target audience: The Dark Crystal had evil Muppets; The NeverEnding Story had a big-ass flying dog; Labyrinth had David Bowie and Jennifer Connelly’s eyebrows. But Return To Oz is, by far, the creepiest of the time period. As its title implies, the film is more or less a sequel to The Wizard of Oz — except, instead of a Technicolor dream world, the titular realm of whimsy is presented as a post-apocalyptic wasteland populated not by charming characters who spontaneously burst into song but creatures out of Sid and Marty Krofft’s worst acid trips. It is much closer to the dark vision of Oz creator (and noted anti-Indian racist) L. Frank Baum than the MGM original (ironically, Return was released by Disney, the company that made its name taking the grim out of Grimm Fairy Tales), which itself frightened a generation of young’uns with its flying monkeys and melting witches. Trust me, though, after witnessing this dystopian nightmare, winged primates suddenly don’t appear all that menacing.

Oldboy (2003)

Actually, this might be a horror movie. It is certainly horrifying, in ways more direct than the other films on this list. And there are moments as gruesome as anything in the Cronenberg-Craven-Carpen-ter oeuvre. But really, Oldboy is an experience completely of its own genre. Helmed by visionary Korean director Park Chan-wook, it’s like a Greek tragedy on crystal meth. When we first meet the protagonist, Oh Dae-su (a mesmerizing Choi Min-sik), he is being kept in a small room against his will by unseen captors for reasons that have never been explained. Somehow, his situation only worsens after he is abruptly released 15 years later. He is determined to extract vengeance from whoever stole the last decade and a half of his life (and framed him for his wife’s murder, too). And so begins the fall. On the way down, Dae-su does some freelance dental work with a hammer, uses said hammer to beat down an entire gang of thugs, and visits a sushi bar to nosh on a still-wriggling squid. None of this, however, can prepare him — or the viewer — for the shock of his ultimate denouement. Admittedly, the plot is slightly convoluted, but it is so vividly, kinetically rendered by Chan-wook, disbelief is not only suspended but blown to bits. And Min-sik helps out by giving one of the most intensely visceral performances this side of Klaus Kinski. Oh, and by the way: Yes, it is a real live squid.