They more and more dangerous stuff they do, the more pleasure they get. Yawning is the body's way of releasing extra carbon dioxide. When you are mentally or physically tired, carbon dioxide causes deep breathing in the throat, and the body expels the carbon dioxide, George Bubenik said. But a yawn also can be a signal between two people, a way of communicating. You take that cue from me, and you yawn too.
People are a lot like animals, and yawning is one way animal herds transmit moods.
A yawn that results from merely thinking about yawning is a subconscious response based on memory. Humans have a great capacity for memory. If you are flying off to somewhere like Europe or Australia, count on it taking a few days for your mind and body to get in sync. Flying through different time zones disrupts the body's perception of time. Bubenik is conducting research on Melatonin, a natural substance.