In zoology, a graminivore (not to be confused with a granivore) is an herbivorous animal that feeds primarily on grass. Graminivory is a form of grazing. These herbivorous animals have digestive systems that are adapted to digest large amounts of cellulose, which is abundant in fibrous plant matter and more difficult to break down for many other animals. As such, they have specialized enzymes to aid in digestion and in some cases symbiotic bacteria that live in their digestive track and "assist" with the digestive process through fermentation as the matter travels through the intestines. Horses, cattle, capybara, hippopotamuses, geese, and giant pandas are examples of vertebrate graminivores. Some carnivorous vertebrates, such as dogs and cats, are known to eat grass occasionally.