"The upper digestive system works just like ours. Food enters the mouth and passes down to the esophagus into the stomach, where the digestive process begins. The chewed up food, mixed with gastric juices (ingesta), then moves into the small intestine. There are two points of interested regarding the upper digestive system. First, rabbits cannot vomit, and second, rabbit teeth continually grow. Grass is highly abrasive, so, if the teeth did not continue to grow, they would be worn away.
LOWER DIGESTIVE SYSTEM -
The lower digestive system deals with food in a special way. Semi-digested good enters the colon from the small intestine, where it is sorted into two parts. Indigestible, large fiber particles are of no further use to to the rabbit, and they are directed straight on through the colon. After water has been extracted, this fibrous materiel emerges as hard fecal droppings resembling raisins. Liquid and non-fibrous particles, however, are are diverted into the cecum. The cecum is, basically, an enormous fermentation chamber (rabbits are "large intestine fermentors"), and it is the powerhouse of the digestive system. Here, the ingesta is fermented by billions of friendly bacteria, releasing otherwise inaccessible nutrients from plant cells. Some of these nutrients are absorbed across the wall of the cecum; the rest are packaged up into the special droppings called cecotrophes, which are eaten by the rabbit as they emerge from the anus."
~Living with a House Rabbit by Linda Dykes and Helen Flack.