According to research, people are more likely to yawn at higher temperatures. When they yawn, the act of stretching their jaws sends more blood to their brain, which can help keep it cool. Also, taking in a big breath of air during a yawn ensures a minor increase in blood flow to the brain. Another theory proposes that yawning is a survival mechanism that increases people’s level of alertness. If someone is getting drowsy and their awareness begins to decrease, yawning may be triggered to keep them from falling asleep.




yawn n. & vi.(打)哈欠

drowsy a. 昏昏欲睡的

keep... from V-ing  使……免於……




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