bhmnscmmTIL yawning is observed in almost all vertebrate animals and is "contagious" across species. There is no consensus on why yawning occurs.
Num10cki thought it was to clear out carbon dioxide build up deep in your lungs, and instinctually its an indicator of rest?
Digestive_BiscuitI always thought it was due to clearing the lungs out or to regulate them but then I saw a turtle yawn under water. I then thought it’s ancestors wouldn’t have been swimmers so maybe it’s instinctive still, but then it would need a mechanism to prevent water inhalation. So why retain the yawn.
Perhaps as you say it’s more about visual communication to others around you.