Why do cows have four stomachs?

Technically, cows only have one stomach, but it’s divided into four compartments because the food they eat (mainly grass) is tough to break down and needs to pass through several stages of digestion. In the first and largest compartment, the rumen, bacteria begin to break the grass down. It then passes into the smallest compartment, the reticulum, where it mixes with saliva to form cud. The cud is then regurgitated back into the cows mouth so it can be chewed some more. In the third compartment, the omasum, water from the grass is absorbed, and then in the final compartment, the abomasum, acids and enzymes break down the food even more.

Cows will often chew their food twice to make it easier to digest