Fistulated/cannulated steer. The cattle are temporarily put to sleep and the plug is surgically implanted. It doesn't hurt them at all, and it allows researchers to study what happens in their stomachs when you feed them different diets. When scientists are done collecting their samples, they can plug the hole so their food doesn't fall out! Cattle have 4 stomach compartments - the rumen is the biggest! When cattle eat foods like hay and grass, the rumen helps them start to break down the starches thanks to helpful bacteria (humans don't have a rumen, that's why we can't eat hay). Then, cattle cough up the mush and "chew their cud" before digesting it a second time - using a stomach just like ours.