Chickens definitely experience pain. But they are good at hiding it. I've learned that a chicken signals pain in several ways. One is to favor the hurting limb by limping or/and pecking at it. When pain becomes overwhelming, it can cause shock, and that will cause the chicken to withdraw and become very lethargic. They quit eating and drinking because they have the instinct that death comes quicker when they stop taking nutrients. That's when you will know that it's time to intervene in the suffering.