<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2017) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2017) (Learn how and when to remove this template message) </Td> </Tr> <P> 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 . </P> <P> The alimentary canal of ruminants, such as cattle, goats, sheep, alpacas, and antelope, are unable to produce the enzymes required to break down the cellulose and hemicellulose of plant matter . Accordingly, these animals have developed a symbiotic relationship with a wide range of microbes, which largely reside in the reticulorumen, and which are able to synthesize the requisite enzymes . The reticulorumen thus hosts a microbial fermentation which yields products (mainly volatile fatty acids and microbial protein), which the ruminant is able to digest and absorb . This allows the animals to extract nutritional value from cellulose which is usually undigested . </P>

What does it mean by chewing the cud