Cud Cud Cud is a portion of food that returns from a ruminant's stomach to the mouth to be chewed for the second time. More accurately, it is a bolus of semi-degraded food regurgitated from the reticulorumen of a ruminant. Cud is produced during the physical digestive process of rumination. The idiomatic expression "chewing one's cud" means "meditating" or "pondering"; similar expressions such as "he chewed that over for a bit", or "chew on that!" likely have the same derivation. The alimentary canal of ruminants, such as cattle, goats, sheep, alpacas, and antelope, are unable to produce the enzymes required to
Chewing Ornithopods, a group of dinosaurs including the Hadrosaurids ("duck-bills"), developed teeth analogous to mammalian molars and incisors during the Cretaceous period; this advanced, cow-like dentition allowed the creatures to obtain more nutrients from the tough plant life. This may have given them the advantage needed to usurp the formidable sauropods, who depended on gastroliths for grinding food, from their ecological niches. They eventually became some of the most successful animals on the planet until the Cretaceous–Paleogene extinction event wiped them out. The process of chewing has, by analogy, been applied to machinery. The U.S. Forest Service uses a machine called