The ostrich (Struthio camelus) is the largest and heaviest living bird. The ostrich or common ostrich is either one or two species of large flightless birds native to Africa, the only living member of the genus Struthio, which is in the ratite family. Ostriches are the fastest runners of any birds or other two-legged animal and can sprint at over 70 km/hr, covering up to 5m in a single stride. Their running is aided by having just two toes on each foot (most birds have four), with the large nail on the larger, inner toe resembling a hoof. When threatened ostriches run although their powerful, long legs can be formidable weapons, capable of killing a human or a potential predator like a lion with a forward kick. The ostrich has the largest eye of any land animal, measuring almost 5 cm across, allowing predators such as lions to be seen at long distances. Ostriches have three stomachs – lacking teeth, ostriches swallow pebbles to grind their food and an adult ostrich carries about 1kg of stones in its stomach. Ostriches can go without drinking for several days, using metabolic water and moisture in ingested roots, seeds and insects, but they enjoy liquid water and frequently take baths where it is available.