The main reason for yawning contagion is psychological, a mimicry of behavior under psychological influence. When the body is in a tired and sleepy state, or when it has not spoken for a long time and the carbon dioxide level in the blood is high, the lack of oxygen in the brain stimulates the respiratory center to expel carbon dioxide and replenish oxygen through yawning. In the same space, see other people yawn, will produce a subconscious reaction, just like seeing food, or other people eat, he or she will be hungry, so see other people yawn, but also realize that he or she needs to replenish the oxygen, all will appear yawning behavior. When a person is under stress, or lack of sleep, there will also be symptoms of yawning, if the frequency of yawning is too high, it is recommended to consult a doctor in a timely manner, to exclude organic diseases, under the guidance of the doctor for treatment.