The rattlesnake's rattle and the derived muscles that shake it present an evolutionary conundrum. Tradition has held that rattlers arose on the Great Plains, where accidental treading from large mammals was a real danger, but genetic mapping points to an origin in the American Southeast, severely shaking that theory. The first rattles probably enhanced an already existent tail-thrashing behavior used in courtship, battle, head-mimicry or other defense. It seems likely, though, that proto-rattlers lured prey with their tails before ever warning away foes. Recently, the viper Pseudocerastes urachnoides was described. The elaborate mock-arachnid at the end of its tail gives us an idea of what rattlesnake ancestors might have looked like.