I usually yawn when I am bored and that is sometimes very difficult to withhold especially in a conference or if somebody explains something to you. I probably always had my mouth open at school, or at least very often.
I also yawn when I wake up but not when I am tired. Should be the other way around. When I was a young girl, I found it funny to yawn, because I had discovered that it is contagious. But in 1508, already, Erasmus wrote, "One man's yawning makes another yawn"
One person yawns and suddenly the others follow, maybe not all, but still a lot. That's the same when you are in a shop and you stare at the ceiling, you can be sure that in a few minutes everybody will lift their heads and look at the ceiling too.
When my cats yawn, I have to yawn too !
Much more as when a human yawns.
We all have learned to put our hand over our mouth when we yawn. Often people forget this and you can see their plumbed or golden teeth or holes in their mouths. Sometimes the mouth is so wide open that one has the impression that he could see outside the other end.
Apparently yawning is healthy because you inhale a lot of oxygen, unless you are in a smoke filled or in crowded room.
Please try not to yawn !
Linking to Linda G. Hill SOCS-Yawn