Final answer:
Cows and buffaloes chew when not grazing because it is a part of their digestion process, where they regurgitate partially digested food known as cud to be chewed thoroughly, aiding the breakdown of cellulose.
Step-by-step explanation:
Ruminants like cows and buffaloes are often seen chewing continuously even when they are not actively eating because this is part of their digestion process. Specifically, the correct answer to why they chew even when not grazing is C) It helps them regurgitate and digest their food. Ruminants have a unique digestive system with a multi-chambered stomach, which includes the rumen, reticulum, omasum, and abomasum. The process of digestion for ruminants involves initially ingesting food and storing it in the rumen, where it partially breaks down before being formed into cud. This cud is then regurgitated back into the mouth, where animals like cows and buffaloes chew it thoroughly to further break down the fibrous plant material. Once the cud is properly chewed, it is swallowed again and continues through the rest of the digestive system, where nutrients are absorbed and waste products are eventually excreted.