I noticed one chicken did not run away from me one day. I poked it and still it stayed still. I picked it up to check it out and liquid came pouring out of its mouth. I separated it from the rest of chickens, it died 3 days later. I noticed it vomited bile colored stuff. It didn't eat hardly and only drank a little. It also seemed a little skinny. Hope its not contagious. No other chickens sick. What could this be. How does it happen. Anyone?