When an offensive post appears on social media, a user can flag it, block it, or mute it. But thousands upon thousands of violent, racist and explicit posts never make it to your screen, thanks to a hidden industry of moderators combing through the worst of the web. Sarah T. Roberts, co-director of the Center for Critical Internet Inquiry at UCLA, joins host Krys Boyd to talk about the people on the front lines of offensive content — and the emotional toll it takes. Her new book is called “Behind the Screen: Content Moderation in the Shadows of Social Media” (Yale University Press).