Where we see a pretty pattern of dark brown links on a pale gold background, chain dogfish literally see each other in a different light. They are one of only a few shark species that exhibit biofluorescence. That is, they glow in the dark. In the deep ocean, where only blue light penetrates, a mystery pigment in the sharks' skin absorbs the blue light and re-emits it in a fluorescent green pattern. Our eyes can't see it, but the sharks' can, helping them to identify each other in the dark ocean.