I have been known to yawn at shall we say “inappropriate” times.  It gives the impression that I’m not interested in the conversation or that I’m bored in general.  But now I know why and it’s the perfect cover for the conventional wisdom. 

A PhD of Princeton University suggests yawning does not occur because you are tired, bored or even need oxygen. Instead, yawning helps to regulate the brain's temperature by cooling it.

I can tell my fellow conversationalists that I am so engaged as to be overheating and need to cool down the old brain!  At least that is the theory.

Not unlike a conventional computer, the brain is sensitive to temperature changes and operates best when they are cool.

The hypothesis people think the walls of the human maxillary sinus flex during yawning like a bellows, which in turn facilitates brain cooling