a semicircle across the river. The most dominant crocodile eats first. Their ability to lie concealed with most of their bodies under water, combined with their speed over short distances, makes them effective opportunistic hunters of larger prey. They grab such prey in their powerful jaws, drag it into the water, and hold it underneath until it drowns. They also scavenge or steal kills from other predators, such as lions and leopards (Panthera pardus). Groups of Nile crocodiles may travel hundreds of meters from a waterway to feast on a carcass. They also feed on dead hippopotamuses (Hippopotamus amphibius) as a group (sometimes including three or four dozen crocodiles), tolerating each other. Much of the food from crocodile stomachs may come from scavenging carrion, and the crocodiles could be viewed as performing a similar function at times as do vultures or hyenas on land. Once their prey is dead, they rip off and swallow chunks of flesh. When groups are sharing a kill, they use each other for leverage, biting down hard and then twisting their bodies to tear off large pieces of meat in a "death roll". They may also get the necessary leverage by lodging their prey under branches or stones, before rolling and ripping. The Nile crocodile possesses unique predation behavior characterized by the ability of preying both within water, where it is best adapted, and out of it, which often results in unpredictable attacks on almost any other animal up to twice its size. Most hunting on land is done at night by lying in ambush near forest trails or roadsides, up to 50 m (170 ft) from the water's edge. Since their speed and agility on land is rather outmatched by most terrestrial animals, they must use obscuring vegetation or terrain to have a chance of succeeding during land-based hunts. In one case, an adult crocodile charged from the water up a bank to kill a bushbuck (Tragelaphus scriptus) and instead of dragging it into the water, was observed to pull the kill further on land into the cover of the bush. Two subadult crocodiles were once seen carrying the carcass of a nyala (Tragelaphus angasii) across land in unison. In South Africa, a game warden far from water sources in a savannah-scrub area reported that he saw a crocodile jump up and grab a donkey by the neck and then drag the prey off.