A bird of prey flies through the skies of Europe and spots a snake on the ground below. Travelling at high speed and soaring at great height, it has mere seconds to decide if it should attack. If the snake is harmless, it could end up with a nice meal. If the snake is venomous, it could get a fatal bite. How can the bird tell the difference? The shape of the head provides a clue.

All of the dangerously venomous snakes in Europe are vipers, like the adder or the horned viper. And all of them have a triangular head. The shape is so distinctive that you can easily recognise these snakes from a distance. And some harmless species like