Beavers have two other sacs, one on each side of the urogenital opening, which secrete an oil. The animal rubs this oil into its fur to repel water. Because its front teeth never stop growing, a beaver must continually cut wood to offset incisor growth. The upper and lower incisors are the primary cutters. A beaver can close its lips behind its incisors to gnaw on and transport saplings while underwater.
Beavers eat vegetable matter.
They prefer soft plant foods, including grasses, ferns, mushrooms, duckweed, algae, and the leaves, stems, or roots of water plants such as cattails and water lilies. When soft foods are available, beavers cut down few trees unless they're needed for dam or lodge repair. They also eat the bark, twigs, and buds of aspen, maple, willow, birch, black alder and black cherry trees. In autumn, beavers cut branches, twigs and small logs, carry them to the bottom of their home ponds, and anchor them in the mud. Then when the pond freezes over in the winter, they still have access to food.