A ruminant is a placental mammal that chews cud - plant matter that has been partially digested and regurgitated.

Cows, goats, sheep, deer, buffalo, giraffes and antelope are all ruminants.

Ruminants belong to the order Artiodactyla, or even-toed ungulates. An ungulate is a mammal that has hooves.

When a ruminant chews its cud, it is said to ruminate - a word that also means to "chew something over" mentally.

A ruminant can digest cellulose, or fiber. This allows it to survive solely on food sources like grass and leaves.

Human beings are unable to digest cellulose.

Ruminants have long, thick tongues.

A ruminant has no incisors - teeth with straight cutting edges that are used to bite and tear food - in its upper jaw.

In place of its top incisors, it has a thick pad known as a dental pad.

There is a large amount of space between the dental pad and its back teeth.

The ruminant can wrap its tongue around a large wad of grass and fit it in the gap between its dental pad and the back teeth. It can pinch the grass between its bottom incisors and dental pad, and then cut off a chunk of grass by swinging its head.

A ruminant has four stomachs: the rumen, the reticulum, the omasum and the abomasum.

Some biologists say that there is only one stomach, which is divided into four compartments.

The rumen and the reticulum together are known as the reticulorumen, or forestomach.

The reticulorumen contains a large number of bacteria that secrete enzymes. These enzymes allow the ruminant to digest cellulose.

After a ruminant chews its food for the first time, it passes through the esophagus, or gullet, and then enters the rumen.

The rumen has space for storing large amounts of food.

Small packets of food pass from the rumen to the reticulum.

The partially digested food then moves back to the mouth, where it becomes cud.

The cud is chewed, and then passed to the omasum.

Within the omasum, powerful muscles grind up the food even more

The food finally passes to the abomasum, also known as the "true stomach." This is similar to the stomach of a non-ruminant. The abomasum secretes enzymes that digest food.

Finally, the food is passed on to the intestines, where digestion is completed.