The sound you hear when you yawn is called a “contagious yawn“.
An involuntary exhaling air often accompanies yawning through the mouth and nose with an audible sound.
This “contagious” sound may be related to the need for more oxygen since it’s often heard in response to fatigue or sleepiness (as well as boredom).
Some research suggests that these sounds could also be part of our innate behavioral repertoire: Even newborn babies make similar sounds when exposed to similar conditions (such as being exposed to bright lights).
And yawning has been shown to increase alertness and help you stay focused, which is why we often yawn when bored or tired.
It also stimulates your parasympathetic nervous system, which controls your body’s rest-and-digest response.
This can help you slow down and feel more relaxed.
Moreover, some researchers believe that contagious yawning happens because we’re so attuned to each other’s feelings — not just because we’re tired.
Why do we yawn?
The most common explanation is that getting more oxygen into our systems is a way to increase alertness and improve brain function.
Therefore, yawning is a sign that your body needs more oxygen.
It happens in response to fatigue, boredom, or stress.
And yawning stretches our lungs, allowing us to take deeper breaths when we need them most — like after running up a flight of stairs.
There are also several theories about why we yawn, including:
Excitement
Some research suggests that yawning may be a sign of interest rather than fatigue or boredom (though this has been disputed).
According to this theory, when you’re excited by something new and interesting, your body tries to take in as much oxygen as possible to help you process what’s happening around you.
This could explain why we often yawn when trying something new or challenging for the first time (like learning something new).
Thermoregulation
Another study found that people were more likely to yawn when they thought about the cold weather than when they thought about the hot weather outside (even though both groups were tested in the same room).
The researchers suggested that yawning might help keep our brains cool when it gets hot out by increasing blood flow through our brains — which releases heat from our bodies into the air around us.
Cognitive function
Yawning may also be related to how we think.
One study found that people who tend to think abstractly are more likely to have contagious yawns than those who prefer concrete thinking.
Other research also suggests that people may be more likely to yawn after reading an emotional passage from a book than an unemotional one.