In the wild, it is not always easy to evaluate at a glance a zebra' state of health. Because of their digestive system that produce a lot of gas from the cellulose digestion processes, zebras usually look well and with a round belly, even when they are weak or sick. So one of the most reliable way is to look at the mane. If a zebra is in good health, its mane is upright. Otherwise, it tends to flop over.