The beaver's front feet are dexterous, allowing them to grasp and manipulate objects and food, as well as dig. The hind feet are larger and have webbing between the toes, and the second innermost toe of the hind foot has double nails used for grooming. Beavers can swim at ; only their webbed hind feet are used while the front feet are tucked under the chest. On the surface, the hind limbs thrust alternately while underwater they move simultaneously. Beavers are awkward on land but can move quickly when frightened. They can carry objects while walking on their hind legs. The beaver's distinctive tail consists of a conical, muscular, hairy base; and a flat, scaly end that makes up two-thirds of the appendage. The tail has multiple functions; it provides support for the animal when it is upright (such as when chewing down a tree), acts as a rudder when it is swimming and stores fat. It also has a countercurrent blood vessel system which allows the animal to lose heat in warm temperatures and retain heat in cold temperatures.