Before commercial dog foods were available, pet owners fed their dogs the parts of animals that humans didn't eat. Green tripe, or ruminant stomach tissue, was often found in a dog's dinner, because it's too stinky for human consumption. Today, green tripe is making a comeback among raw-diet proponents.
Green tripe isn't actually green -- the term just means it's raw and unprocessed. While the "green tripe" is actually brown, it might retain a greenish tinge if the animal ate grass shortly before slaughter. As stomach tissue, it contains good intestinal bacteria, which can help your dog's digestion. It contains digestive enzymes and amino acids. Mixing some green tripe into your dog's food helps maintain intestinal health. While people think it stinks to high heaven, dogs find the odor intoxicating and usually gobble it up.
Giving your dog large chunks of green tripe can help clean his teeth, as the rubbery texture makes chewing it a long-term process. Just make sure he's enjoying it outdoors, not in your house. It won't do much for his breath, at least for a while.