Sunbeam Snake. A beautiful, iridescent snake which spends most of its time burrowing underground.
Iridescence is a kind of structural colouration. It comes from the microscopic structure of the scales, rather than any pigments.
This structure interferes with light to create iridescence, but it also reduces the friction of the scales. Iridescence is a by-product of many reptiles who carve their path underground.