A guard of honour member of the Wanita UMNO party yawns as she awaits the arrival of Malaysian Prime Minister for the UMNO General Assembly in Kuala Lumpur, on Wednesday, November 7 2007.
It can catch you embarrassingly unawares - as Wanita Umno Members has discovered.
But rather than being a precursor to sleep, scientists say the yawn is actually designed to keep you awake.
A study has found that when you yawn, the inhaled air reduces the temperature of vessels in the nasal cavity, allowing cooled blood to be sent to the brain.
This chills the brain, making it more alert and able to perform better.
Yawning is the way we COUNTER sleep. A yawn defends against sleep. It accompanies a release of unconsciousness, a lessening of the dark energy threatening to overwhelm you, a draining of the engulfing.