Regurgitation is the back flow of undigested food into your dog’s esophagus or even mouth. It requires little or no active effort by your dog other than perhaps a cough or hack. It is in contrast to vomiting which is a forceful ejection of undigested food or stomach contents in which you will generally observe your dog’s belly heaving with the expulsion effort. Regurgitation typically indicates a problem with your dog’s esophagus and should be assessed by a veterinarian.