Have you ever been convinced you heard a voice -- shout, a whisper, someone speaking directly to you -- only to turn around and realize no one was there? This experience is more common than we might comfortably imagine. For millennia, people who heard voices in their heads were considered prophets, lunatics, or vessels of infernal forces. In tonight's episode, Ben, Matt and Noel explore the nature of this particular paracusia -- ultimately learning modern science still struggles to understand what may well be a conspiracy within your own brain.