There's more to yawning than meets the eye. Research shows that yawning is contagious. And so when you see the word "yawn," or look at photos of people mid-yawn, or watch film of actual yawns, you will start to feel like yawning.
Also, the more you're affected by the images, the more empathic you are. So if you're feeling the need to yawn right now, then you tend to be good at reading other people's emotions, whereas if you don't feel like yawning, then you're more of an emotional island.
And so, if you want to gain a fun insight into your friends, just ask them to watch this video and see if they yawn.