Let’s cut to the chest: Ridley Scott’s 1979 sci-fi horror masterpiece “Alien” is forever remembered for one indelible scene — a “very significant moment in film history,” genre director Gary Sherman says — the chest-burster sequence, when a gore-slimed, serpentine creature chews its way out of the torso of a hapless John Hurt while he’s having dinner, leaving him a quivering, blood-drenched corpse and unleashing the title monster to slither away and torment the rest of the spaceship’s unsettled crew for the next hour.

Great detail and respect are granted this monumental moment in Alexandre O. Philippe’s dizzyingly in-depth, intellectually exhaustive documentary “Memory: The Origins of Alien” — from wild talking-head theories (Hurt is literally giving birth!) to gruesome behind-the-scenes footage of this greatest of gross-outs.

One of those talking heads, author Ian Nathan, deftly parses the visceral and dramatic importance of the scene: “The chest-burster changes the complexion of the film from a kind of epic to a kind of horrible, horrible intimacy that’s claustrophobic and inward. Suddenly everybody is trapped. Suddenly the spaceship is small and confined” and the film becomes a primal survival story. Which, I say, renders “Alien” such a splendid, fearsomely realistic haunted house tale during a grisly second half that vibrates with unendurable tension and dread.

“Memory” makes a strong point that the mythos and monster in “Alien,” which was written by sci-fi fanatic Dan O’Bannon, were hardly original. “‘Alien’ didn’t come out of a creative vacuum,” we’re told. “It drew from a whole heritage of American science fiction.”

O’Bannon cherrypicked sources over the years, including comic books, H.P. Lovecraft’s horror fiction, and B-movies like “It! The Terror from Beyond Space” (1958), Howard Hawks’ “The Thing from Another World” (1951), “Planet of the Vampires” (1965) and, most extensively (and strangely), Roger Corman’s lurid “Queen of Blood” (1966). 

But it was O’Bannon and director Ridley Scott’s mutual exposure to the lithograph “Necronomicon,” a phantasmagoria of wondrous and hideous creatures by Swiss surrealist artist H.R. Giger, that cemented the look and language of “Alien.” Scott rhapsodizes about the titular creature, sometimes known as the Xenomorph: “This is beautiful, not just threatening, and it also has very sexual connotations. It’s like a rather beautiful, humanoid bio-mechanoid insect.”

Giger himself did some artistic cherrypicking, synthesizing Egyptian mythology, dream imagery, Boschian fright-scapes, medieval dragons, Hindu goddess Kali and, key to the chest-burster, the disturbing canvasses of British artist Francis Bacon. “Giger consolidates every monster from every mythology from around the world into a single creature. It embodies the mythic Other,” USC professor Henry Jenkins says.   

Why “Alien” works so well is its commitment to the kind of gritty realism of so much superior 1970s American cinema. An Altmanesque naturalism permeates the film, and it boasts gorgeous Kubrickian photography, a crack cast of virtual unknowns, deliberate pacing and adult restraint. 

It is, simply, an art film. It spurned the space-western kicks of “Star Wars” and the Keane-eyed aliens of “Close Encounters” (both 1977). Suddenly we were served a new, naturalistic depiction of outer space in the sooty, clanky, eerily rain-soaked cargo ship Nostromo, a floating industrial city, a grungy “space truck,” that fatefully investigates a distress signal beamed from an alien planet. 

“Memory” is fascinating when talking about artistry and craft, but veers onto shaky ground when its commentators argue too hard that “Alien” is a product of its social and political times or, almost laughably, gaze at the film through a scrim of academic feminist theory. Says one: The movie is a “male fantasy of the kind of oppression that had been handed out to women over the century of guilt that was part of masculinity.” (Where’s the chest-burster when we need it?)

Fortunately the focus stays mostly on the allegory and mythology behind this iconic, massively influential movie, and the obsessive density of it all is both boggling and breathtaking. The film “can mean many, many, many things,” says writer William Linn, conceding, “I don’t think we can get to the bottom of ‘Alien.’”

“Memory: The Origins of ‘Alien’” hits theaters and VOD on October 4. Trailer HERE.