This is how I explain it. When I first started scuba diving and explained to the instructor that it wasn't an issue to pop my ears, he was kind of horrified and was like no don't yawn underwater to do that. He didn't seem to understand, no matter how many times I explained it, that I can do it without actually yawning. You just like... mimic the start of a yawn. And then can continue it into a full actual yawn if you want to.