It's something so natural that we take it for granted -- but when you think about it, it's a little strange. Why does water come out of our eyes? And why does it happen when we're happy? Or sad? Or scared? Or exhausted? In this episode we dive into our mysterious emotional tears, find out why onions make us cry (and how to stop it), and hear about the eye-protecting trio of tears that makes Eyetropolis a safer place. Plus: Our Moment of Um explores why we sweat when we're nervous.