Yawning is the most common involuntary activity of opening the mouth wide and breathing in deeply to fill in the lungs with air.

Why do we yawn?
Some evidence suggests that yawning is a means of communicating changing environmental or internal body conditions to others. Still, low oxygen levels in the paraventricular nucleus (PVN) in the hypothalamus of the brain can induce yawning.
When we are bored or tired, we just don’t breathe as deeply as we usually do. As this theory goes, our bodies take in less oxygen because our breathing has slowed. Therefore, yawning helps us bring more oxygen into the blood and move more carbon dioxide out of the blood.

Is yawning contagious?
About half of adults yawn after someone else yawns due to a universal phenomenon called “contagious yawning.” Contrary to popular belief, a new study from Duke University suggests that contagious yawning is not strongly related to variables like empathy, tiredness, or energy levels.
Scientists refer to this as a type of an “echo-phenomenon.” In other words, it’s an automatic imitation of another person. An auto response in the area of the brain that’s responsible for motor function of the body.