Q. Cows swallow their food once and then this food goes back to the mouth to be chewed again. How can this phenomenon be explained?

The food ingested by cows and other ruminant animals passes first within two compartments of the digestive tube called the reticulum and the rumen. Within them the food suffers the action of digestive enzymes released by microorganisms that live there in mutualist ecological interaction, in the reticulum the food is separated in some food bolus too. After passing the reticulum the food (cud) is regurgitated to the mouth to be yet again chewed and swallowed in a process called rumination. The digesting food then enters the omasum where it is mechanically mixed after that the food goes to the abomasum the organ where the chemical digestion takes place after leaving the abomasum (the true stomach) the food bolus gains the intestine.