Regurgitation is the expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.

Regurgitation is used by a number of species to feed their young. This is typically in circumstances where the young is at a fixed location and a parent must forage or hunt for food, especially under circumstances where the carriage of small prey would be subject to robbing by other predators or the whole prey is larger than can be carried to a den or nest. Some birds species also occasionally regurgitate pellet

Pellet (ornithology)

A pellet, in ornithology, is the mass of undigested parts of a bird's food that some bird species occasionally regurgitate. The contents of a bird's pellet depend on its diet, but can include the exoskeletons of insects, indigestible plant matter, bones, fur, feathers, bills, claws, and teeth...

s of indigestible matter such as bones and feathers. Penguins

Penguin

Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...

 are known to regurgitate in order to feed their young ones.

It is in most animals a normal and voluntary process unlike the complex vomiting

Vomiting

Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...

 reflex in response to toxins.

In humans

In humans it can be voluntary or involuntary, the latter being due to a small number of disorders. Regurgitation of a person's meals following their ingestion is known as rumination syndrome, a rarely diagnosed eating disorder. It may be a symptom of gastroesophageal reflux disease

Gastroesophageal reflux disease

Gastroesophageal reflux disease , gastro-oesophageal reflux disease , gastric reflux disease, or acid reflux disease is chronic symptoms or mucosal damage caused by stomach acid coming up from the stomach into the esophagus...

 (GERD).

A subset of people, most current or former bulimics, are able to regurgitate without using any external stimulation or drug, by means of muscle control. Practitioners of yoga

Yoga

Yoga is a physical, mental, and spiritual discipline, originating in ancient India. The goal of yoga, or of the person practicing yoga, is the attainment of a state of perfect spiritual insight and tranquility while meditating on Supersoul...

 have also been known to do this. Professional regurgitators

Professional regurgitator

A professional regurgitator is an entertainer whose act consists of swallowing and regurgitating various unusual objects. The objects may consist of anything from live animals , to light bulbs, billiard balls and kerosene .Some magicians perform regurgitation as part of their act , but professional...

perfect the ability to such a degree as being able to exploit it as entertainment.