Despite its cute common name, the pumpkin toadlet is actually a very poisonous frog. Its bright colors are a warning sign—a biological phenomenon called aposematism. But it turns out the frogs, native to the Atlantic forest along the coast of Brazil, have been keeping their niftiest feature to themselves. When Sandra Goutte, a postdoctoral associate at NYU Abu Dhabi, and her colleagues "discovered that Brachycephalus ephippium could not hear its own mating calls, they searched for alternative visual signals the frogs could use to communicate instead," according to a press release. They shined a UV light on the hoppers, and were surprised to find their backs glowed. Turns out, the pumpkin toadlet's skeleton is unusually fluorescent, according to the new research published Friday in the journal Scientific Reports. Because their skin is so thin, the UV lamp actually hit the bones of the two specimens under analysis, triggering that eerie gleam.