Although flightless, emus have vestigial wings, the wing chord measuring around 20 cm (8 in), and each wing having a small claw at the tip.[1] Emus flap their wings when running, perhaps as a means of stabilising themselves when moving fast.[2] They have long necks and legs,[33] and can run at speeds of 48 km/h (30 mph) due to their highly specialised pelvic limb musculature.[32] Their feet have only three toes and a similarly reduced number of bones and associated foot muscles; emus are unique among birds in that their gastrocnemius muscles in the back of the lower legs have four bellies instead of the usual three.