Chicken did not come out of coop this morning. Slime on beak and in mouth. Hangs head and jerks neck as if trying to dislodge something. Crop feels empty, nothing obvious in neck when I straighten it. Bird mostly just standing in one place head held normal most of the time some times down as it opens and closes mouth and jerks. Did not notice problem yesterday. Does not eat or drink seems weak and distracted with trying to "get something out". Help! Advice please. These are free range birds. ON The bird is some times violently shaking its head and neck.