Believe it or not, that's a common trait with all of us! I found some information over at Listverse.com that sort of explains this exercise!
A yawn is a natural human reflex. It involves the inhalation of air, stretching of the eardrums, and is followed by a large exhalation of breath. Yawning is associated with tiredness, stress, lack of stimulation, and boredom. It is one of the most bizarre human functions. Yawning can be infectious and is triggered by seeing others yawn, hearing a yawn, or talking on the phone with someone who is yawning. A number of theories have been proposed that attempt to explain why animals yawn, but nothing has been substantiated. One theory states that yawning occurs when a person’s blood contains an increased amount of carbon dioxide and needs oxygen. However, other studies show that yawning decreases oxygen intake.
Another theory states that yawning is a person’s way of controlling brain temperature. It has been suggested that a yawn can reduce or increase blood pressure in the brain. This theory has been supported by the fact that people get a desire to yawn while making a drastic change in elevation. Another speculated reason for yawning is the desire to stretch one’s muscles. Contagious yawning may be a way of keeping a group of animals alert. It may be an instinctual reaction from one member of the herd to the next, reminding everyone to stay alert. Anecdotal evidence suggests that yawning helps increase the state of alertness.
Interesting Fact: It is possible that yawning is a territorial reflex, a process that is meant to make the body appear bigger by stretching out the arms and opening the mouth. When animals are witnessed yawning, the human reaction is to become aware of the creature’s teeth and fighting potential.
It's nice to know that we share this reflex with animals. After all, they beat us out with nearly everything else.
Now, I have fresh coffee on the patio and some fresh baked white bread to go with it! No yawning, please!