Filmmaker Coralie Fargeat is fascinated by butts. “The Substance,” her Cannes-winning gross-out joke about an aging Hollywood actress with a high threshold for self-inflicted pain, boasts more butts per minute than a chainsmoker’s ashtray, a feat all the more monumental for the film’s nearly 21⁄2-hour running time. Be they spandex-wedgied or jiggling nude, each is caressed by the lens with the same hunger a burger commercial has for its buns.

Point made: In this body-horror flick, a human’s only worth is as meat. With fearless, ferocious leads Demi Moore and Margaret Qualley willing to let the camera chop them into chunks of flesh — lips, calves, hair, wrinkles and, yes, keisters — for a film that prioritizes shocks over plot, get ready for a whole lot of their blood and guts too. The story is simple.

Former star Elisabeth Sparkle (Moore) is too old to continue hosting televised aerobics, the last stop on her slide out of the industry. Once, Elisabeth had talent. She even won an Academy Award if you believe the mutterings of her boss, Harvey (Dennis Quaid), who, in the spirit of the film, grumbles, “Oscar winner, my ass.

” But that was so long ago even Elisabeth’s forgotten she’s more than a set of toned thighs. Elisabeth’s solution is a solution — a green goo called the Substance — that cleaves her cells in two and grows a second, youthful her who climbs out of her back and takes over her existence. When her alternate, Sue (Qualley), sashays into.