When spent layers are finally killed, about half are slaughtered for human consumption and used in soups, pot-pies and other processed foods where their bruised and battered bodies can go unnoticed. The others are ground up alive, manually decapitated, crushed, composted, or otherwise discarded because with an abundant supply of meat birds on the market, slaughterplants have little or no use for them."
Inevitably, the blade misses some birds who then proceed to the next station on the assembly line: the scalding tank. According to USDA statistics, millions of birds every year have their bodies submerged in scalding hot water (about 143° F) while they are fully conscious. According to Virgil Butler, a former Tyson slaughterhouse worker, 'When this happens, the chickens flop, scream, kick, and their eyeballs pop out of their heads. Then, they often come out the other end with broken bones and disfigured and missing body parts because they've struggled so much in the tank.'"
The full article, with references, is here.
Christians and Jews: The Bible says that it's wrong to prevent an ox from eating grain when he is threshing (separating grain from stalk), because that would be psychologically cruel. When you buy eggs, or products made with eggs, you are supporting a form of cruelty that is similar to one forbidden in the Bible.