"Animals" looks at how animals use blue. Besides pigment, animals produce blue through the careful creation of structures that mainly reflect blue light. Harder to explain was why animals use blue, or colours in general. It was initially thought that colour was used just for camouflage. Later on, the idea that colours are used as a warning signal emerged. Then came the idea that colour is also used as a signal for fitness in mate selection. Unfortunately, humans preferences and desires for blue animals have driven some species to the edge of extinction.