i was thinking about the yawning thing, and i came up with
If you are in a room, and your brain is not getting enough oxygen, could it be that there isnt as much oxygen in the room? Not like the moon or something, but a small enough amount less, to make you yawn. Therefore, other people in the same room, hence, breating the same oxygen deficient air, would need to yawn as well.
Can you make people yawn over the phone? i guess that would blow my theory. haha.