Why do we cry when we yawn sometimes?
960960
That face muscle is connected with the eyes.
313997
There are two possible reasons for tears to be released when you yawn. \nThe tears are secreted by the "lacrimal glands" located just inside the eye \nlids next to the nose. These glands secrete the fluid into the "lacrimal bag" \nwhere it is then released through the "lacrimal ducts" into the lining of the \neye lids to keep the eye moist.\n\nWhen you yawn it is possible that there is pressure put on the "lacrimal \nbag" and some fluid is forced out. \n\nThe secretion of the "lacrimal glands" is under control of the autonomic \nnervous system. This nervous system controls all the involuntary functions \nas contrasted to the somatic nervous system that controls all purposeful \nactions. When you reach out to catch a ball it is the somatic system that \nactivates the muscles to acheive that action. The autonomic system \ncontrols such things as the heart beat, sweating and the function of the \nintestines.\n\nWhen the autonomic portion of the nerves are activated the "lacrimal \ngland" secretes the tears which appear at the eye. These nerves also \ncause the pupil of the eye to constrict and get small as well as to cause\nthe glands in the nose to secrete. So, when you are crying you get tears,\na watery nose and your pupils should constrict. Perhaps the act of \nyawning causes activation of these nerves. Next time you yawn look in \nthe mirror and see it your pupils get small. But don't get too close to the \nmirror because when you look at things close to you the pupils get smaller \nanyway.
380194
CRYING IS A WAY OF LETTING OUT OUR  DEEP FEELINGS.BY CRYING IT DOES NOT MEAN THAT YOU'RE WEAK,ITS IS JUST AN ACT OF POURING OUR FEELINGS WHEN WE ARE DEPRESSED OR SAD.AFTER CRYING DEFINITELY IT FEELS BETTER AND RELIEVED
586280
We don;t necessarily know why humans yawn, whether its to increase oxygen intake, equalize barometric pressure...  We're not sure.  While you're asleep, however, the environmentmay not change all that much, and your body doesn't need a yawn to readjust.  If the reason we yawn is for increased oxygen, then the slower, deeper breaths keep the blood oxygen at an acceptable level.  If it's because of the barometric pressure, presumably it's not changing rapidly enough to force our bodies to make a gross adjustment like on an airplane.  If it's for another reason that we yawn... Well, I guess the sleep state preserves that, too.
1159613
Ahhh... the age old question. lol\n\nThere are a number of theories. One is that when someone yawns, they take oxygen out of the air, and we need the oxygen so we yawn to get the oxygen we need. I'm not sure about that one. I think its just a joke.\n\nA more likely theory is that it relates back to the herd instinct. You know, monkey see, monkey do.
213862
Why we yawn when we see others yawning has baffled scientists for ages and a number of suggestions have been put forward to explain this phenomenon. What we do know is that yawning is an involuntary action- our brain does it without us thinking about it, even very young babies yawn showing that it's a built in action (Chimps do it too by the way). Just thinking about yawning can trigger the bit of the brain that causes a yawn.  http://www.ratlab.co.uk/yawn.htm\n\nMore theories can be found at the links below:
824759
Why?  -  Because it a state of expression of feelings. You can cry of joy or sadness.\n\nHow?  -  Hiccup cry, laugh cry, just cry - there are many ways to cry.
15668
~~Ya this happens to every one...every single human being as well as animal! This is normal...when there is oxygen shortage in our lungs or when we feel relax we yawn. So dont worry and start yawning!~~
635799
1. because your body needs oxygen\n2. becaus you are bored and it is a way for your body to tell you to do something else\n3. becaus other people yawn. it is a social behavior that makes a group "stay together" \n\nhow? not sure, but I think your brain open your mouth and make your lungs draw in lots of air without letting you know first.
397407
Though the other answers are right (that yawning occurs to signal tiredness when the brain demands extra oxygen due to slipping performance), I would like to add another related comment.\n\nI recently read in the newspaper that scientists are discovering that yawning is a signal of compassion.  Researchers conducted studies in which participants watched videos of people yawning and the researchers measured the time between the yawn of the person on the video and the ensuing yawn of the study participant.  They then somehow effectively linked this elapse to compassion; what they stated was that the quicker you yawn after you see someone else yawn, the the more compassionate you are.\n\nRegretfully, I don't know the web address of the article, which I found intriguing, but I think it is worth your time to investigate.
217186
In humans, and probably in all those organisms that yawn, yawning is caused by a lack of oxygen. When we are tired, we breathe less often as well as less deeply, so our bodies have evolved a way to fix that problem: forced deep breathe.
304410
I can't remember where I heard this but someone told me it's an empathetic response. Like the more in tune you are to others feelings, the more likely you are to yawn when you see someone else do it.
632459
Causes of yawning\n1.An indication of tiredness, stress, over-work or boredom. \n2.An action indicating psychological decompression after a state of high alert. \n3.A means of expressing powerful emotions like anger, rejection or apathy. \n4.A sign that one is not breathing deeply, and not receiving enough oxygen through the body. \nA yawn can express strong anti-social messages, and so in some cultures people try to mute or mask them by placing a concealing hand over the yawning mouth.\n\nA long-standing hypothesis is that yawning is caused by an excess of carbon dioxide and lack of oxygen in the blood. The brain stem detects this and triggers the yawn reflex. The mouth stretches wide and the lungs inhale deeply, bringing oxygen into the lungs and hence to the bloodstream. It is almost certain however, that this hypothesis is not correct. One study documented that this effect does not exist ("Yawning" by Robert R. Provine, pages 532-539, American Scientist, November-December 2005, Vol 93, No. 6). A 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. Conversely, a greater presence in the brain of opiate neurotransmitters such as endorphins, reduces the frequency of yawning. Patients taking the serotonin reuptake inhibitor Paxil (Paroxetine HCl) have been observed yawning abnormally often.\n\nAnother theory is that yawning is similar to stretching. Yawning, like stretching, increases blood pressure and heart rate while also flexing many muscles and joints. Some have observed that if you try to stifle or prevent a yawn by clenching your jaws shut, the yawn is unsatisfying. As such, the stretching of jaw and face muscles seems to be necessary for a good yawn.\n\nThe yawn reflex is often described as contagious: if one person yawns, this will cause another person to "sympathetically" yawn.[2] The reasons for this are unclear; however, recent research suggests that yawning might be a herd instinct.[3] Other theories suggest that the yawn serves to synchronize mood behavior among gregarious animals, similar to the howling of the wolf pack during a full moon. It signals tiredness to other members of the group in order to synchronize sleeping patterns and periods of activity. It can serve as a warning in displaying large, canine teeth, thus proclaiming, "don't attack while I am sleeping..." The contagion of yawning is interspecific (i.e., try yawning in front of your dog). Yawning in public is generally regarded as impolite in the West, but came into fashion in polite French society for a brief period in the late 18th century. Oddly, sometimes sympathetic yawning may be caused by simply looking at a picture of a person or animal yawning, or even seeing the word "yawn".\n\nAdelie Penguins employ yawning as part of their courtship ritual. Penguin couples face off and the males engage in what is described as an "ecstatic display," their beaks open wide and their faces pointed skyward.
317540
A Yawn is the brain's natural way of rapidly increasing the amount of oxygen taken into the lungs for use by the body during times of fatigue. It is triggered by very delicate mental cues and accordingly, can be triggered by seeing someone else yawn or even thinking about yawning long enough.
1177906
Yawning is your body's attempt to get more oxygen.  When you are tired, your breathing tends to get more shallow, and your body tries to compensate by making you yawn - bringing in more oxygen.\n\nHere's some more information on yawning, and why it's "contagious".
272413
It is an instinctual social response.  Yawning signals to others in the social group that it is time to rest.
450975
the act of yawning squeezes the tear glands