Ask why this is important to know. The abomasum is the true stomach. The lighter food collects in the rumen. The abomasum is the true stomach with typical enzyme action. The food remain here for a relatively short time compared with the time in the rumen.
Rumination is the regurgitation, remastication, resalivation, and reswallowing of food.
The purpose is to further smash and break up the less digestible parts of food. The small intestine is a long coiled tube connecting the stomach with the large intestine. Take 3 pieces of paper, tape them together and fold them accordion style, so that when laid on the table they are the same length as one normal sheet. Show the students both, then stretch out the larger one. Ask why it is good to have a folded lining in the intestine, which can only be so long in an animal's body.