The least weasel has a thin, greatly elongated and extremely flexible body with a small, yet elongated, blunt-muzzled head which is no thicker than the neck. The eyes are small in relation to their head size and are bulging and dark colored. The legs and tail are relatively short, the latter constituting less than half the body length. The feet have sharp, dark-coloured claws, and the soles are heavily haired. The skull, especially that of the small "rixosa" group, has an infantile appearance when compared with that of other members of the genus "Mustela" (in particular, the stoat and kolonok). This is expressed in the relatively large size of the cranium and shortened facial region. The skull is, overall, similar to that of the stoat, but smaller, though the skulls of large male weasels tend to overlap in size with those of small female stoats. There are usually four pairs of nipples but these are only visible in females. The baculum is short, , with a thick, straight shaft. Fat is deposited along the spine, kidneys, gut mesentries and around the limbs. The least weasel has muscular anal glands under the tail, which measure , and contain sulphurous volatiles, including thietanes and dithiacyclopentanes. The smell and chemical composition of these chemicals are distinct from those of the stoat. The least weasel moves by jumping, the distance between the tracks of the fore and hind limbs being .