Hairball

A hairball is a small collection of hair or fur formed in the stomach of animals, and uncommonly in humans, that is occasionally vomited up when it becomes too big.

Hairballs are primarily a tight elongated cylinder of packed fur, but may include bits of other elements such as swallowed food.

Due to the fragility of their digestive systems, hairballs in rabbits must be treated immediately or they may stop feeding and ultimately die from dehydration.

A trichobezoar is a bezoar (a mass found trapped in the gastrointestinal system) formed from the ingestion of hair.

These hairballs occur when hair strands collect in the stomach and are unable to be ejected due to not enough friction with the surface of the gastric mucosa.

Example of the sounds and motions a common housecat makes when it is coughing up a hairball.
A 10 cm (3.9 in) cat hairball
A 5 cm (2.0 in) cat hairball