North American beaver large, webbed hind feet. The unwebbed front paws are smaller, with claws. The eyes are covered by a nictitating membrane which allows the beaver to see under water. The nostrils and ears are sealed while submerged. A thick layer of fat under its skin insulates the beaver from its coldwater environment. The beaver's fur consists of long, coarse outer hairs and short, fine inner hairs (see Double coat). The fur has a range of colors, but usually is dark brown. Scent glands near the genitals secrete an oily substance known as castoreum, which the beaver uses to waterproof its fur.
Hyraceum and ages until it becomes a fairly sterile, rock-like material (also referred to as "Africa Stone") that contains compounds giving it an animal, deeply complex fermented scent that combines the elements of musk, castoreum, civet, tobacco and agarwood. The material is harvested without disturbing the animals by digging strata of the brittle, resinous, irregular, blackish-brown stone; because animals are not harmed in its harvesting, it is often an ethical substitute for deer musk and civet, which require killing or inflicting pain on the animal. After it has been fossilized hyraceum has been used as a traditional folk medicine in South