When you scroll through Facebook or Twitter, you expect to see photos of friends’ recent vacations, well-wishing birthday posts and Buzzfeed articles about porcupines eating pumpkins. What you don’t expect are graphic images of child pornography or videos of people having their heads cut off. Though many of us don’t know it, a vast labor force of content moderators, largely based overseas, works day and night to keep our social media feeds free of this sort of offensive material.