Regurgitation resembles vomiting and is due to problems with the esophagus e.g. obstructions, collapsed esophagus and some systemic disorders. Vomiting quickly leads to dehydration. The appearance of the vomitus (undigested, partially digested) and the time between feeding and vomiting helps narrow down the causes.
If the vomit contains food, it indicates how long the food has been in the stomach. Mucus and fluid may be gastric or may be swallowed saliva. Yellow or green vomit is a sign of bile in the stomach. Fresh blood (amount varies from small flecks to large amounts or blood clots) indicate severe infection, internal injury or a blood clotting disorder. An appearance of coffee grounds is partially digested blood.
Occasional regurgitation immediately after a meal may be due to greed. However, swift veterinary help is needed, if kittens are vomiting. They will need treatment for dehydration and possibly subcutaneous fluids.