Japan’s tiger keelback snake eats toxic toads and stores the toxins in specialised organs on the backs of their necks called nuchal glands. If a snake is threatened it arches its neck, making the nuchal gland area more prominent. A predator that bit the snake’s neck would probably get a mouth- or face-full of the fluid from the glands, which would be distasteful or even painful. But not all keelbacks exhibit this defensive behavior. Snakes from a toad-free island flee when attacked, rather than standing their ground. Now it seems the snakes know when they do and don’t have toxins.
Read the whole story at New Scientist: This Snake Knows How Toxic It Is And Fights Only When Armed.