Of course a vampire is simply a cannibal with good table manners, and "Ravenous'' is a darkly atmospheric film about an epidemic of flesh-eating and the fearsome power that it brings. It takes place during the Mexican-American War, in an isolated U.S. Army outpost in the Sierra Nevadas, when a half-dead man (Robert Carlyle) staggers into the fort with the story of snowbound travelers, starvation and worse: "We ate the oxen, then the horses, then a dog, then our belts and shoes ... .'' Eventually one of the party died of starvation, and they ate him. Then they ate others ... and by now the commander of the fort has heard enough, and determines to send out a party to investigate. All of this is shown in dark colors and a soundtrack of chimes and mournful cries; low, ominous, burbling percussion, and far-off female laments. "Ravenous'' is the kind of movie where you savor the texture of the filmmaking, even when the story strays into shapeless gore.