The Boomslang ( Dispholidus typus) the most venomous snake in Africa. You need less Boomslang Venom to kill a man than any other African Snake. It is part of the Deadly Dozen Snakes of South Africa.
These snakes settle down in captivity and become rather tame. This snake is showing no signs of distress or threat.
The threat display of the Boomslang includes the snake swaying from side to side, inflating it's neck with air ( rather like a balloon) and striking with speed.
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From @mambaman