yawning
n. the act of drawing in through the mouth a volume of air that is much larger than that inhaled in normal respiration, serving to improve oxygen supplies to the brain. Some research indicates that yawning is mediated by the same neurotransmitters in the brain that affect emotions, mood, appetite, and so forth (i.e., serotonin, dopamine, glutamic acid, and nitric oxide). The more of these compounds that are activated in the brain, the greater the frequency of yawns. Yawns can be a form of nonverbal communication in that they are contagious and can indicate boredom or disagreement as well as sleepiness.