Asked by: Richard Wainsley, King's Lynn
Snake venom is made by organs that evolved from salivary glands. Ordinary saliva contains enzymes to help digest food as you chew it and natural selection has favoured snakes that include ever more toxic enzymes in their saliva.
Scientists at Bangor University recently sequenced the genome of the king cobra and found that the toxins in its venom are slight variations of ordinary proteins. As prey gradually evolved immunity, so snakes have responded with a complex mix of 50-100 different proteins to alter blood pressure, prevent blood clotting and paralyse nerves.
Get more fascinating Q&As from BBC Focus magazine by following @sciencefocusQA