Bison eat grass by wrapping their tongue around it and pinching it off between their tongues and lower teeth. They swallow their food practically whole. Bison are ruminants. Ruminants have stomachs made up of four compartments which help them digest food. When eaten, food is first stored in the rumen , the first compartment of the stomach.
Some food goes directly to the second compartment which is the reticulum.
Eventually, all the food goes to the second compartment, the reticulum . Here stomach juices and bacteria begin to break food down and form it into cud. When the bison are resting, muscles in the reticulum push the cud back up into bison's mouth. There the cud is chewed and mixed with more saliva. Then the cud is swallowed again to be further digested.