It is called the picnic line: 18 workers lined up on both sides of a belt, carving meat from bone. Up to 16 million shoulders a year come down that line here at the Smithfield Packing Co., the largest pork production plant in the world. That works out to about 32,000 a shift, 63 a minute, one every 17 seconds for each worker for eight and a half hours a day. The first time you stare down at that belt you know your body is going to give in way before the machine ever will.