Richard Linklater's film "Fast Food Nation" ends on the killing floor, as cattle march placidly up a ramp to be slaughtered. We see them shot and shackled, sliced and diced. Grey loops of intestine come sweeping down the conveyor belt like some demented version of "The Generation Game." Inside the cinema at Cannes, the audience groaned and covered their eyes. Linklater is known for his gentle, Gen-X movies. Now he's taking on the American meat industry with his latest movie. He talks with Xan Brooks.