Stick your tongue out!

[OakLeaf]

I was taught to put the tip of my tongue on the roof of my mouth, right behind the teeth.
Do it now.

NOW, I said!
See how that works?

What's it supposed to do? In airway terms, to me, it completely prevents breathing through my mouth.

I was taught to do that while doing supine abdominal exercises, actually. It helps you use your abs and not your neck muscles to lift your head. How it works, I have no idea, but it does.