One of the really cool things that we did at the Junior Boiler Vet Camp was getting to stick our arms into a cow's rumen. If you were wondering, the whole in Buttercup's side doesn't hurt her and it actually saves other cows because she gives rumen fluids to cows in need. Also, when we all had our arms in her, she couldn't feel that either! It was mostly just chewed up grass because there aren't any digestive acids in the rumen, and we could also feel the rumen rotating and moving. It was a really neat experience.