For most of the nineteenth century, naturalists assumed that the brilliant coloring of certain frogs was meant to attract mates, on the reasonable principle that beauty in nature serves reproduction. The puzzle was that these frogs were also conspicuously easy for predators to spot—an apparent contradiction that the mating theory could not resolve. The breakthrough came when a young researcher reversed the question: instead of asking whom the color attracted, she asked whom it warned. The frogs, she found, were poisonous, and their brightness was not an invitation but a threat, advertising to predators that a meal would be the eater's last. The color had been speaking all along; the naturalists had simply assumed the wrong audience.