SO THESE TWO GUYS walk into a bar. No—this is a true story! One is a neuroscientist (yours truly), and the other is a writer for Scientific American Mind. (We'll call him Bill.) We are at the recent meeting of the Society for Neuroscience in Atlanta. A gentle bear of a man comes over, licking suds from his lips and praising the local brew with an authoritative German accent. As he raises his glass to the light to inspect the beer's clarity, I think to myself, “This is my chance.” So I tell him about a bizarre thing my eyes do.