Kiboko grooming a crocodile. I have seen this behaviour on a regular basis and believe the hippos groom the crocodiles for a couple of reasons. The area they choose to groom is normally the tail or along the ridge on the top of the croc’s body. In those areas quite a lot of hippo dung can accumulate when the croc is swimming in the river or even when on land and the hippos defecate. They often cover the crocs in dung. So a hippo will smell the scent of the bull on the croc and hence grooms it. The other reason may be because there are some kind of salts or minerals in the crocodile’s skin. Whatever is the case the croc will lie there quite content until the hippo has finished. Up to fifteen minutes is the longest I have recorded this. The hippo always gives a huge gape at the end of the grooming session.