Puff-adder (Clotho or Echidna arietans), one of the most venomous and dangerous vipers of South Africa. Its popular name refers to its habit of puffing itself up when irritated. It attains a length of 4 or almost 5 feet, and is often as thick as a man's arm. Its head is very broad; its tail suddenly tapered; its colour brown, chequered with dark brown and gray or white. The puff-adder is very sluggish, and often lies half buried in the sand of the desert, its head alone being raised above ground. Its poison is used by the Bushmen for their arrows. The River-jack (Clotho nasicornis) is also South African; the male bears a scaly spine between the nostrils.