Here’s what I know:
For whatever reason, it’s impossible to breathe while doing this.
it’s much easier to do it with your eyes closed.
I’m pretty sure the roar isn’t blood because I can’t hear a heartbeat or any real change in the sound.
Finally, whatever I’m doing makes my closed eyes vibrate.
I suspect what is happening is somehow I’m making my sinuses expand while my throat is closed.
Sorry if I sound insane.