> If an animal is drowsy or bored, it will be less alert than when fully awake and less prepared to spring into action. "Contagious" yawning could be an instinctual signal between group members to stay alert.

> Anecdotal evidence suggests that yawning helps increase a person's alertness.

> Paratroopers have been noted to yawn during the moments before they exit their aircraft.

https://en.wikipedia.org/wiki/Yawn