A venomous viper (family Viperidae), about 1 m long and sometimes longer, with a stout body, rounded snout, and body colour that is generally dull but varies geographically. The snake is sluggish and mostly nocturnal and lies well-camouflaged as it waits to ambush its vertebrate prey. It occurs throughout sub-Saharan Africa, Yemen, and south-western Saudi Arabia, except for in rainforests, deserts, and high mountains. It is probably the most common snake in Africa. When disturbed it hisses loudly and can strike very fast, delivering extremely toxic venom.