 It changes the way that your jaw looks. For a guy, it gives a square chisel look, which is supposedly what a lot of women always want in their guys. So you press your whole tongue against the roof of your mouth, keep your lips together, breathe through your nose, and maintain a straight posture. They also have metal things that they sell that you can put in your mouth and all do this. But in case you're wondering, who's behind this trend? I thought this was fascinating.