Hippopotamuses are animals with enormous jaws, that spend most of their time in water. They can often be seen poking just their eyes, nose and mouth, which are all lined up on the top of their head, out of the water to check what is happening around them. Hippos are unable to perspire, so their skin secretes a natural substance that is red. This secretion is sometimes referred to as “blood sweat”, and protects the hippo’s skin from the sun and from bacteria. Wild hippos are ferocious animals, and often attack humans or other animals who invade their territory.