Why is Yawnig So Contagious?

Yawning commonly occurs when we are tired or drowsy. People also yawn when they are bored. Why do we yawn and what is its exact purpose is still an unresolved mystery. Everyone yawns - babies to adults, even the animal’s yawn, and in fact it can be noted as early as in an eleven or twelve week’s old fetus in the womb.   
Yawn is an involuntary body reflex related to the respiratory tract of the body controlled by our spinal cord and the hypothalamus region of the brain. Yawning increases the oxygen content of the blood and makes a person more alert.

There are many theories about why we yawn  - like it gets rid of excess carbon-di-oxide from the body or it cools our brain etc but the last word is still to be written on the subject. It lasts for about 6 to 8 seconds.
The temperature theory may explain yawning in animals as it is believed that it works like a radiator among birds. If the air is cool the birds yawn and this helps the brain to cool off and alters the blood flow. Apparently it works by cooling off the brain in humans too. Some studies equate yawning to a 'heightened state of arousal' so when we yawn it may function like it providing an extra cup of coffee or tea giving as a jolt of extra energy.

This may also explain why when we are tired or exhausted we tend to yawn as exhaustion and sleep deprivation increases brain temperatures.

There are  few diseases where one may yawn more than others and  these includes - Anxiety, Cerebral tumor, End Stage Liver Failure, Epilepsy, certain drug withdrawal effects like codeine and morphine. Excess yawning may indicate the onset of epilepsy or migraine is some patients.

However what makes yawning an interesting subject is that it is very contagious.  Dr. Seuss in her Sleep Book wrote - "A yawn is quite catching you see. Like a cough. It just takes one yawn to start other yawns off."

Why is yawning so contagious no one knows. The other contagious human behavior is laughter and why we laugh is another subject to write about... but unlike yawning we do know for sure that there are benefits of laughter which are both physical and psychological.   

Even while reading about yawning you may have already yawned a couple of times. Tell us how many times did you yawn while reading this little trivia on the subject.

How many times did you yawn while reading the article?

Once
Twice
Three
Four
More than four