The rare Iranian spider-tailed viper (Pseudocerastes urarachnoides) waggles a fake "spider" - actually a fleshy lure with leg-like scales at the tip of its tail - to tempt birds within striking distance. Until 2001, the viper was known only from a single misidentified specimen collected during a U.S. expedition to Iran in 1968. The weird structure on its tail was so unlike anything documented in other snakes that it was written off as a birth defect or an abnormal growth. While scientists had suspected its unique tail was used for luring prey, new observations of the dramatic bird captures now confirm this. The new study also revealed the viper starts growing its tail lure after birth, and that it isn’t complete until adulthood.