The polar bear's most common hunting method is called "still-hunting": the bear uses its excellent sense of smell to locate a seal breathing hole, and crouches nearby in silence for a seal to appear. The bear may lie in wait for several hours. When the seal exhales, the bear smells its breath, reaches into the hole with a forepaw, and drags it out onto the ice. The polar bear kills the seal by biting its head to crush its skull. The polar bear also hunts by stalking seals resting on the ice: upon spotting a seal, it walks to within , and then crouches. If the seal does not notice, the bear creeps to within of the seal and then suddenly rushes forth to attack. A third hunting method is to raid the birth lairs that female seals create in the snow.