What is the term for partially digested food that some animals can regurgitate and chew a second time?

The correct term for partially digested food that some animals can regurgitate and chew a second time is "cud." This process is characteristic of ruminant animals, such as cows, sheep, and goats. These animals have a specialized stomach structure that allows them to break down tough plant materials through fermentation. After initial digestion, the food is returned to the mouth as cud, where it is further chewed to aid in digestion, allowing for better nutrient absorption.

Other terms in the choices do not pertain to the process of secondary chewing of food. Semen refers to the reproductive fluid in males, feces is the waste material eliminated from the body after digestion, and enzymes are biological catalysts that facilitate chemical reactions but do not describe a physical substance that can be chewed or digested. Thus, "cud" is specifically linked to the unique digestive strategies employed by certain animals, making it the correct answer.