That is a Symbiotic Relationship, like how birds will clean a crocodile's teeth for them. The birds eat whatever meat is left stuck in its teeth, and the crocodile won't have infections from the stuck meat. Same with water buffalos and birds, the birds get a free meal and the water buffalo don't have ticks and parasites. And another one is a zebra and ostrich, it's a somewhat odd one but still the same. Zebras have poor eyesight while the ostrich has poor hearing. So they travel together so the ostrich can stop the zebra's enemies while the zebra will hear the ostrich's enemy.