Scientists have a pretty solid understanding of how viruses and other contagions are passed among us. It’s still a mystery, though, that behavior also seems to be contagious. Science journalist Lee Daniel Kravetz joins us to talk about why we sometimes mimic one another, which he writes about in “Strange Contagion: Inside the Surprising Science of Infectious Behaviors and Viral Emotions and What they Tell Us About Ourselves” (Harper Wave).