Hippos spend the hottest hours of the day in water. Indeed, their skin is made of a thin epidermis, very sensitive to dehydration. When the animal stays exposed to the sun for too long, the mucous glands of its skin produce a kind of red liquid that acts as a protection. This is also a first warning for this animal, before its skin starts crackling. An excessive exposure to the sun, without hydration, for instance in case of drought, may be fatal.