Glass frogs live in South America and their bodies are almost entirely transparent. The reason they have these transparent bodies is to help protect them from predators, specifically predators looking up into the leaves. Their blood contains a pigment that is necessary to ferry oxygen around your body. You can't get rid of that pigment because then you wouldn't be able to get any oxygen anymore. So there's only so far you can evolve away pigment. However, the glass frogs have got a new trick that has just been discovered by researchers which is genuinely baffling.