Female black rhinos are smaller than the male black rhino, but both male and female black rhinos both have two horns. Black rhinos have a distinctive hooked lip, unlike the white rhino. The horns are made of keratin, the same substance as fingernails. Rhinos have thick skin that helps protect them from thorns. They also have wide-rotating ears that can easily detect sounds in the savannah. Finally, their sense of smell is superb in sensing predators.