The cheetah, with its long legs, deep chest and narrow waist, help to make it is easy to see why this is the world's fastest land mammal (to 68 mph). The extremely flexible spine permits long bounds while running, and wide nostrils allow sufficient entry of air into the lungs to facilitate the great speed. The muzzle is short and the eyes set high on the head. The nostrils are wide, and the ears small and rounded. The claws do not retract fully and are partially exposed to give traction during fast turns and rapid acceleration. The short, coarse fur is tawny yellow with round black dots. The cheetah has distinctive "tear-lines" running from the inner corners of the eyes to the outer corners of the mouth. Head and body length is from 44 to 53 inches, the tail from 26 to 33 inches, and the weight ranges from 86 to 143 pounds. Cheetah cubs under 3 months of age have a "mane" of blue-gray hair on the nape of the neck and the back.