This has always fascinated me. This is also not at all unique to humans. I have a cavy (Guinea pig, she had a cage mate but the cage mate passed) and she had a

This has always fascinated me. This is also not at all unique to humans. I have a cavy (Guinea pig, she had a cage mate but the cage mate passed) and she had a bladder stone. It was really big. After she passed it with some assistance from the vet, she got a really bad infection. Apparently, the stone cut her up on the way out. She had to go on antibiotics for quite a while and the medicine killed off her gut flora. This made a mess, made her really uncomfortable, and it smelled. So, I needed to figure stuff out. There were three steps really. First, she needed medical food to make sure she was getting everything she needed. Second, she had to take some benebac, and third as cavies are coprophagic, I got some poop from a healthy pig and mixed it in to some of her food. She recovered and seems to be happier and more calm than ever. Gut bacteria is apparently super important in every mammal. No idea about birds, reptiles, or arthropods or fish.