'I hear the most beautiful sound in the world,' says Dr. Bruce Means. He is referring to the call of a toad that he and his expedition team - North Face Climber Mark Synnott and National Geographic contributing photographer Joe Riis - traveled to the tops of the Tepuis of South America to find. Means has a hypothesis that he calls a paradigm shift and this little toad is the missing link. In this short film, the team braves the elements and first time repels into crevices in search of this illusive pebble toad. If they find this toad, will they make it back out of the crevice? The expedition to the Tepuis was made possible by National Geographic Expeditions Council.