THE HARDEST PART to watch in American Mustang lasts only a second. It's a shot of a grim slaughterhouse—empty, but dungeon-like, it's made all the more painful by its presentation as a place where wild, gorgeous horses meet their inglorious end. It's there and gone in a flash, almost subliminal, couched in a film that's otherwise light on stomach-churning details, palatable to young American girls drawn to the romance and drama of a horse's life—who may end up being these animals' most powerful advocates.

Part Daryl Hannah-voiced documentary, American Mustang is spliced with the mini-tale of a wild horse being tamed (as one of those wistful country girls looks on). Mustang is educational in service to activism, circling urgently around the fact that there are more wild horses in government facilities than there are on public land. Private cattle herders see them as pests, compelling the Bureau of Land Management to round them into traps using low-flying helicopters. As government property, they're basically just stored, trucked around to various facilities, and all too frequently, the film alleges, sold to slaughter for as little as 10 bucks a head.

It's not really fair that horses should be held above any other animal led to slaughter, but Mustang knows they are. Americans reserve an awe for horses that runs deep in our heritage. "Real men don't eat horses," drawls one of the film's ranchers, and killing a horse is about as noble in our imagination as drowning a sack of puppies (pigs are smarter than either of them, but bacon).

The fact that most Americans aren't aware of what population control for wild horses means at the hands of a benign-sounding government entity is what Mustang is betting on for well-aimed, bipartisan outrage. And it's shrewd to keep it family friendly; those headstrong American girls don't shine to messing with horses.