Rabbits have large digestive tracts because they must consume a lot of plant matter to get enough food. Mostly grasses and forbs (herbs other than grasses), their diet is heavy on cellulose, which is difficult to digest. Rabbits use two distinct types of feces to solve this issue: hard feces and soft, viscous black pellets, the latter of which is consumed right away (see coprophagy).

The large cecum, a secondary chamber between the large and small intestines that contains a large number of symbiotic bacteria that aid in the digestion of cellulose and also produce certain B vitamins, is where chopped plant matter accumulates. Here, the soft feces form and can have five times as many vitamins as the hard feces.

They are digested by the rabbit in a special part of its stomach after being excreted. This process of double digestion ensures that rabbits get the most nutrition out of the food they eat by allowing them to use nutrients that they might not have used during the first passage through the gut.