Why do we yawn and when we do why do our eyes water?
441318
Yawing is caused by lack of oxygen i think.
41848
I have a theory on this to share.\nMay be yawning is not a chain reaction at all.\nIts just our reaction to the state of things, outside as well as inside our body.\nFor instance, we feel sleepy when our brains are tired or refuse to process. Result is that we all yawn when after a tired game, after a boring speech.\nMay be even when there is lack of sufficient oxygen.\nWe all have different reaction times though. Thats probably the reason why its being mistaken to be a chain reaction.
153961
Do your eyes only get watery when you wake up?  You could be responding to dry air or it's possible that you have an allergy.  You may want to see your eye doctor to see what he/she recommends.  If it's an allergy, you may need some special eyedrops to help alleviate the symptoms.
288559
A yawn is a reflex of deep inhalation and exhalation associated with being tired, with a need to sleep, or from boredom. \n\nThe yawn reflex is often described as contagious: if one person yawns, this will cause another person to "sympathetically" yawn. The reasons for this are unclear; however, recent research suggests that yawning might be a herd instinct.\n\nHerd instinct\n------------\nThe so-called herding instinct is a social tendency in humans to identify with and model many behaviors and beliefs after a larger group of individuals with whom they identify.\n\n\nOther 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...
56870
The dictionary tells us that yawning is caused by being fatigued, drowsy or bored, scientists are discovering that there is more to yawning than what most people think. Not much is known about why we yawn or if it serves any useful function, and very little research has been done on the subject. However, there are several theories about why we yawn.\nThe Physiological Theory -- Our bodies induce yawning to drawn in more oxygen or remove a build-up of carbon dioxide. This theory helps explain why we yawn in groups. Larger groups produce more carbon dioxide, which means our bodies would act to draw in more oxygen and get rid of the excess carbon dioxide. However, if our bodies make us yawn to drawn in needed oxygen, wouldn't we yawn during exercise? Robert Provine, a psychologist at the University of Maryland, Baltimore County, and a leading expert on yawning, has tested this theory. Giving people additional oxygen didn't decrease yawning and decreasing the amount of carbon dioxide in a subject's environment also didn't prevent yawning. \nThe Evolution Theory -- Some think that yawning is something that began with our ancestors, who used yawning to show their teeth and intimidate others. An offshoot of this theory is the idea that yawning developed from early man as a signal for us to change activities. \nThe Boredom Theory -- In the dictionary, yawning is said to be caused by boredom, fatigue or drowsiness. Although we do tend to yawn when bored or tired.
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.
14485
At the corner of our eye is a tube leading to the nose, at the top of which is a small container called a lachrymal sac. This sac is full of tears. When we yawn the muscles in our face squeeze this sac and tears spill out from the eyes.  This also explains why your nose runs when you cry.
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.
748622
It could be that that particular eye is dry, sometimes when our eyes or one eye is dry the body compensates by sending more water to the dry part of the body thus causing it to water.  Try seeing your doctor to make sure nothing out of the ordinary is going on inside of you.\n\n\nHope this helps
1069354
Because when you need sleep is when you need more oxygen intake, and by yawning that brings in more oxygen.
757509
sometimes if your eyes are really dry, it stings when your eyes water,  you should put eye drops in them to water them up
414151
What's behind this mysterious epidemic of yawning? First, let's look at what a yawn is. Yawning is an involuntary action that causes us to open our mouths wide and breathe in deeply. We know it's involuntary because we do it even before we are born. Research shows that 11-week-old fetuses yawn. \n\nThere are many parts of the body that are in action when you yawn. First, your mouth opens and jaw drops, allowing as much air to be taken in as possible. When you inhale, the air taken in is filling your lungs. Your abdominal muscles flex and your diaphragm is pushed down. The air you breath in expands the lungs to capacity and then some of the air is blown back out. \n\nWhile the dictionary tells us that yawning is caused by being fatigued, drowsy or bored, scientists are discovering that there is more to yawning than what most people think. Not much is known about why we yawn or if it serves any useful function, and very little research has been done on the subject. However, there are several theories about why we yawn. Here are the three most common theories: \n\n\nThe Physiological Theory -- Our bodies induce yawning to drawn in more oxygen or remove a build-up of carbon dioxide. This theory helps explain why we yawn in groups. Larger groups produce more carbon dioxide, which means our bodies would act to draw in more oxygen and get rid of the excess carbon dioxide. However, if our bodies make us yawn to drawn in needed oxygen, wouldn't we yawn during exercise? Robert Provine, a psychologist at the University of Maryland, Baltimore County, and a leading expert on yawning, has tested this theory. Giving people additional oxygen didn't decrease yawning and decreasing the amount of carbon dioxide in a subject's environment also didn't prevent yawning. \nThe Evolution Theory -- Some think that yawning is something that began with our ancestors, who used yawning to show their teeth and intimidate others. An offshoot of this theory is the idea that yawning developed from early man as a signal for us to change activities. \nThe Boredom Theory -- In the dictionary, yawning is said to be caused by boredom, fatigue or drowsiness. Although we do tend to yawn when bored or tired, this theory doesn't explain why Olympic athletes yawn right before they compete in their event. It's doubtful that they are bored with the world watching them. \nThe simple truth is that even though humans have been yawning for possibly as long as they have existed, we have no clue as to why we do it. Maybe it serves some healthful purpose. It does cause us to draw in more air and our hearts to race faster than normal, but so does exercise. There's still much we don't understand about our own brains, so maybe yawning is triggered by some area of the brain we have yet to discover. We do know that yawning is not limited to man. Cats, dogs, even fish yawn, which leads us back to the idea that yawning is some form of communication. \n\nHave we provoked a yawn out of you yet? If we have, hopefully it's not out of boredom, but by the power of suggestion.
56869
The answer is, no one really knows why yawning is "contagious". Or why we yawn at all. One popular explanation is that yawning allows you to get rid of too much carbon dioxide in your system and increase your oxygen supply. This was disproved by Dr. Robert Provine and his research team in 1987.\n\nNow scientists are wondering if yawning is from our deep past -- part of our evolutionary history. Did a yawn signal to the group that it was time for everyone to retire to the trees and snooze? Did a yawn signal that we were all feeling cozy and warm about each other? Did a yawn signal something more like, "Gee, I know how you're feeling, I feel that way too."
510901
Dr. Barry Make, a pulmonologist at National Jewish Medical and Research Center in Denver, says the answer is not because we are tired or bored — although that’s the common perception. Read on for his explanation.\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\nTHE 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. Studies 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).\n\nNext time you're in a meeting, try this little experiment: Take a big yawn, cover your mouth out of courtesy, and watch and see how many people yawn. There's a good chance that you'll set off a chain reaction of yawns. Before you finish reading this question of the day, it's likely that you will yawn at least once. Don't misunderstand, we aren't intending to bore you, but just reading about yawning will make you yawn, just as seeing or hearing someone else yawn makes us yawn. \n\nInteresting Yawning Facts\n•The average yawn lasts about six seconds. \n•Your heart rate can rise as much as 30 percent during a yawn. \n•55 percent of people will yawn within five minutes of seeing someone else yawn. \n•Blind people yawn more after hearing an audio tape of people yawning. \n•Reading about yawning will make you yawn. \n•Olympic athletes often yawn before competition. \n\nWhat's behind this mysterious epidemic of yawning? First, let's look at what a yawn is. Yawning is an involuntary action that causes us to open our mouths wide and breathe in deeply. We know it's involuntary because we do it even before we are born. Research shows that 11-week-old fetuses yawn. \n\nThere are many parts of the body that are in action when you yawn. First, your mouth opens and jaw drops, allowing as much air to be taken in as possible. When you inhale, the air taken in is filling your lungs. Your abdominal muscles flex and your diaphragm is pushed down. The air you breath in expands the lungs to capacity and then some of the air is blown back out. \n\nWhile the dictionary tells us that yawning is caused by being fatigued, drowsy or bored, scientists are discovering that there is more to yawning than what most people think. Not much is known about why we yawn or if it serves any useful function and very little research has been done on the subject. However, there are several theories about why we yawn. \n\nHere are the three most common theories: \n•The Physiological Theory -- Our bodies induce yawning to drawn in more oxygen or remove a build-up of carbon dioxide. This theory helps explain why we yawn in groups. Larger groups produce more carbon dioxide, which means our bodies would act to draw in more oxygen and get rid of the excess carbon dioxide. Howeve
213045
There are two basic reasons why eyes water.  Eyes can water if the tear ducts are blocked.  You can have surgery to solve this problem but sometimes the results are less than completely successful.  Tears are also a reaction to something irritating the surface of the eyes.  The irritation can be allergy, air pollution, infection, scratches on the surface of the eye, and even dry eye.
858650
The other two answers are sufficient, but I just want to jump on the band wagon and say the same thing, but I will BS my way through with an elaborate answer so that you may think that I am answering more.\n\nI actually searched the web and found out that most scientists don't know why people yawn. If you are interested, read this short explanation : http://www.madsci.org/posts/archives/aug99/934846431.Gb.r.html\n\nI learned a lot by reading it, I hope it answers your question. You can even e-mail the person about this topic... If you find out, please post the answer and let me know...
499803
It is because after eating the concentration of sugar in the blood increases which leads to ex-osmosis ie movement of water from the body cells to the blood where there is high concentration of solute. The movement of water from the cell results in the reduced metabolism which courses one to feel sleepy.