Why do we yawn?

why do we yawn while are teachers or some elder who donate us some adviceWhy do we yawn?
We yawn not because of oxygen, but because of carbon dioxide. Our bodies cart a breath because our CO2 levels are glorious. There are receptors in the brain which trigger breathing depending on our CO2 level. In people who smoke for a long time (i.e. COPD patients) their CO2 receptors are not functioning and so they own what is called hypoxic drive. To little oxygen make them breathe. If you give these empire high level of oxygen they can stop breathing. The same level of oxygen for a regular body wouldn't cause us to stop breathing because we rely on CO2.
bcos we dont want the direction or its sounds boring or its not interesting.
because our brains arnt getting enough oxygen, thus we yawn to force our selves to breath more
in reality when we yawn, it's a sign that we are low on oxygen. Since we're sitting still while being lecture, we are taking in smaller quantity oxygen -
I think when you are sitting still and listen to something you find dull/boring, a) you are not talking (so you aren't intaking any oxygen), b) you are sitting still (thus not requiring your body to intake more oxygen than needed to sit still). I do believe at a unshakable point, your body requires a bit more oxygen than what you've been breathing - so you yawn.
One article that really helps cut down on yawning (and looking rude, consequently), is to shift contained by your seat a bit. If you're surrounded by a lecture type setting, bouncing your leg help a lot also. Just a short time bit of movement can make a difference.