If your chicken is throwing up, there are a few possible explanations. First, chickens sometimes regurgitate food that they have eaten too quickly. This is usually not a cause for concern and the chicken will typically return to normal eating habits after a short period of time. Second, chickens can occasionally vomit due to an infection or other illness. If your chicken is vomiting more than once or twice, or if the vomiting is accompanied by other symptoms such as lethargy, diarrhea, or a decrease in appetite, you should take your chicken to the vet to be checked out. Third, a chicken may vomit up its crop contents if the crop is impacted or otherwise not functioning properly. If you suspect that your chicken's crop is impacted, you should take your chicken to the vet for treatment.