The Arctic hare's body is built for cold: short ears, a shortened muzzle and a compact trunk that reduce surface area, with fur dense enough to insulate it on bare snow. Winter coats are white in most of the range, but the northernmost populations never turn grey, because their snow season does not end.
The bipedal bounding is well documented on film. A hare rises onto its hind feet and travels several body lengths in an upright hopping run before dropping back to four legs. Proposed reasons include better visibility over uneven snow, keeping the forelimbs clear of crust, or simply the momentary posture of a startled animal in mid-flight. None has been tested properly.
Group behaviour is the other departure from hare stereotype. Arctic hares are usually solitary but aggregate in winter, and gatherings of hundreds have been recorded, which is unusual for a genus generally described as dispersed and asocial.