Vomiting is a result of nausea, being sick to the stomach. Regurgitation is different than vomiting. When a dog regurgitates it is throwing up completely undigested food and it looks much like what the dog just ate. This is usually a result of eating too fast, too much, or having too much exercise right after eating. Vomiting may have food in it or it may just be stomach fluid. A vomiting dog is always a sick dog while a regurgitating dog may not be sick at all.