Hippos have a difficult life. Living most of their time in aquatic environments may sound cool, but it is not very comfortable when you have trouble controlling your weight and do not manage what is going inside your digestive system. In hippos societies, belching is a very common behavior which is normally carried out on land for practical reasons, as avoiding getting drown, and is also a good way to avoid indigestion by expelling gases that have been inadvertently ingested at eating time!
(Or a similar design)