Why do people yawn and stretch?
448287
people yawn when they are bored, not tired\n(dogs yawn when they are under stress)\npeople stretch to get blood flow..\n\ndogs also sneeze when they are happy...try it with your dog...he will sneeze if you sneeze at him
276956
When working out the blood flow is increased to the working muscles. As a result there is less blood and oxygen flowing to the brain triggering the yawn. This is your body's way of increasing the oxygen level in the brain to compensate.\nAs your body accomodates the increased physical demand, the yawning should become less.
17567
Yawning is one of those bodily mysteries that scientists haven't completely figured out yet.  The best theory I could find was that you yawn because you're not getting enough oxygen to the brain (maybe there is a lack of oxygen in the space you're standing).  Whenever you're aware of someone yawning, it activates a reaction in your subconscious mind that acts as a threat response.  Basically, whenever you see someone yawn, it makes you body think there is a shortage of oxygen too, and you yawn in response.  No one knows if this is actually the case, but I think that it is a good theory.
694355
more recent hypothesis is that yawning is used for regulation of body temperature. Another hypothesis is that yawns are caused by the same chemicals (neurotransmitters) in the brain that affect emotions, mood, appetite and other phenomena. These chemicals include serotonin, dopamine, glutamic acid and nitric oxide. As more of these compounds are activated in the brain, the frequency of yawning increases
406589
One theory says that it is a vestige of the group behavioural aspect of human evolution. This theory was put forth following observations of communal yawning in apes. The leader in an ape group yawns, and the rest follow suit. \n\nApart from the theories, consider this: \nTo some extent, yawning is indicative of one's state of mind, and can be physiologically linked to cerebral activity. It usually comes when all novelty in an idea or concept being explored has been temporarily exhausted. So it may happen that when an idea is being explored in a group, a statistical majority would always hit a 'low' (or an intellectually lean) patch in the exploration simultaneously . Hence yawning results. \n\nThe other type of yawning is when there is no group activity involved, and one yawns just by looking at another person yawning. This has to do with empathizing, as has been explained.
300748
WHen you see another person yawning, the message goes across your brain that may be you too needs more oxygen and in attempt to get more air in, you open your mouth wide open, your lungs expand and you yawn. That's why it's called reflex yawning
433222
because they make one tired so then they person that isn't tires suddenly becomes tires and yawns. but yawns shouldn't make one another person yawn because the person is just releasing co2 from their bodies.
309172
padillio is right. it is just a mental thing, and she is also right in saying that it is because of a lack of oxygen. it is also associated with being tired b/c when you're body is fatigued or tired, you're breathing slows down and you get a lack of oxygen. yawning is an involuntary muscle movement to make you breath heavily and take in more oxygen. anyway, that's pretty much it.
33139
we yawn to equalise the pressure difference between our ears and the outside. when u yawn you equalise the pressure in your ears but there is a disbalance created in the atmosphere and hence others around you also start yawning....!!!!
202412
THE TRUTH IS that we don’t completely understand why people, or animals for that matter, yawn. It’s widely assumed that yawning occurs because we are tired or bored or because we see someone else doing it, but there isn’t any hard evidence to support these beliefs.\n\nThe most plausible explanation, and the one that is taught in medical school, is that we yawn because oxygen levels in our lungs are low. \n\nStudies have shown that during normal, at-rest breathing, we don’t use anywhere near our lung capacity; for the most part, we just use the air sacs at the bottom of the lungs. If the air sacs, called alveoli, don’t get fresh air, they partially collapse and the lungs stiffen a bit. As a result, it’s believed, our brain prompts the body to either sigh or take a yawn to get more air into the lungs.\n\nBut certain aspects of yawning remain even more mysterious. Fetuses, for instances, have been observed yawning in the womb, yet it’s known that they don’t take oxygen in through their lungs. And yawning seems to be a symptom of multiple sclerosis and other medical conditions, for reasons unclear.\n\nAnother puzzling phenomenon is that some male animals, men included, yawn in association with penile erection (although it’s presumptuous to assume they’re bored with their sex lives).
378590
People yawn when the level of carbon dioxide in their blood is a little too high, this is bad and eventually can cause unconsciousness.  To stop this you yawn, yawning means you take in a big gulp of oxygen and expel carbon dioxide.  They are thought to be contagious because if I see you yawning my brain thinks.. uh oh there is too much carbon dioxide in this room that person is already feeling the effects, to protect myself I will yawn too!\n\nBy the way you also yawn if you're tired because you're breathing naturally slows which makes carbon dioxide build up more easily.  You will yawn when you are tired to expel this excess carbon dioxide!
680125
Here's a theory. Yawning can be caused by lack of oxygen, and if a bunch of people are in the same room which is poorly ventilated (no windows open, no air conditioning, or it's a stiflingly hot room) they could all yawn because of this, as they are all in the same place.\n\nEither that or they are all tired! :D
1174829
because our bodies are low on oxygen... we yawn to take in a big gulpl of fresh oxygen to awaken our sleepy oxygen deprived brain... you know it does a body good.
481912
scientifically it's because your body forces an action to acquire something, in this case it's OXYGEN. breathe deeper or more constantly. try it. if you breathe like about a quarter of your max breathe every 5 seconds you will yawn after a while.
467214
Yawns are one of the brain's ways of getting oxygen and fighting fatigue. If someone yawns in response to your yawn it's because they are feeling the same fatigue you are.
662014
This came up in my sister's wildlife biology class--in the wild, animals that live in herds do something similar to a yawn when everything is peaceful and there is no danger lurking (like lions), and the yawn passes from one animal to the next as a signal.  Apparently the biological urge is in humans as well--maybe we are passing along that we are relaxed and not feeling threatened.
526472
I learned somewhere that this is a survival thing--if you are yawning, there might be a lack of oxygen or you are about to need a lot of oxygen.  Your yawn alerts others so they supply themselves with oxygen as well.