It's the stomachs of ruminants- cud chewing- animals. It can't be the stuff for human consumption from the grocery store though since they clean and bleach it out. Green tripe is unprocessed so all the digestive enzymes, probiotics, partially digested grass, etc. are still in there. It's very... erm... aromatic, lol. But it must taste wonderful to dogs. I haven't used it since I had to get rid of my freezer when I moved to a tiny apt. but finding a good source was tricky. I think there might be companies who ship... not sure why I never looked into that but there must be. I should look into that for myself now that I think about it.