This snake grows to about 1.5m in length. What is it?

A twig snake, Thelotornis capensis, which waves its body around to look like a twig, then blows its head up to look huge and frightening when threatened

A harmless tree snake, Dendroaspis innocui, suffering from a common virus caught from birds which causes the temporary swelling (oedema)

The Olive Mamba, a relative of the black mamba. It can strike up to 10 times, each time delivering enough venom to kill a dozen men within an hour