Despite its massive bulk, this amphibious mammal moves underwater with grace, and trots on land with surprising speed (2) (4). Indeed, the name hippopotamus means 'river horse', pertaining to this species' semi-aquatic lifestyle (7). An extremely large animal with a round, barrel-shaped body, short legs and a large, broad head. The body is a greyish to muddy-brown colour on top and a pale pink colour underneath (3) (7) (8). The broad mouth can be opened extremely wide to expose large, curved canines, used in aggressive displays (3). The eyes, ears and nostrils protrude on the top of the head, allowing the animal to remain receptive to its surroundings and breathe while otherwise almost totally submerged underwater (3) (4). The hippopotamus' virtually hairless skin is moistened by a secreted pink, oily substance that protects the skin from sunburn and drying, and perhaps infection (2) (3).