Why do some lizards have blue tongues?

A Tonguesrarely come bluer than that of the blue-tongued skink, – a shortlegged, slow-moving, snake-like lizard, found in Australia and a few Melanesian islands. The skink’s earthy-brown coloration provides decent camouflage, but if a predator come close enough to see through the disguise, it changes tactics, opening its mouth wide to display its tongue, which is even more vivid to predators that can see ultraviolet light.

Warning colours are often a signal that an animal is toxic, venomous or aggressive. But in the case of the blue-tongued skink, it’s an empty threat that serves only to startle assailants, akin to butterflies flashing eyespots on their hindwings.