Simultaneous mouth yawning---a coincidence or a reaction?!

Simultaneous mouth yawning---a coincidence or a reaction?

I really don't know why when you yawn there is virtually always someone else next to you yawning at about the same time. It doesn't matter who it is and where, If I yawn someone does it with me. I know there is other people that this happens to, as well.
So can anybody give a clear explanation?
Why at the same time? Can two people be tired enough to yawn at the same time? What determines yawning rate or even simple yawning?

4 weeks ago
Wow, very interesting!!! I mean all of you say you yawned when you read my question. Very interesting!!!! Why did I not yawn, then? I've read it like 4 times.
Well, I think I have to put some of your answers in and figure it out. I really can't give a best answer for this because all of yours are good and interesting. Thanks.

Ever notice how you yawn a lot more when you're bored or sleepy? It's because oxygen wakes up the brain. When you yawn you take in more oxygen. When other people see you yawn, their brains are like "hey, I could use some oxygen too" so they also yawn and it sets off a chain reaction.

It's basically your body's way of balancing the oxygen level in your body.