Yawning(打哈欠) is something we all do—maybe because we're tired or we are not interested in the same old things. Sometimes, just seeing other people yawn can make us yawn, too. But why does it happen like this?

Many of us think we open our mouths when we yawn to take in more air, but in fact it appears there is no clear biological reason. According to BBC Bitesize, a new research suggests it might be because yawning cools the brain(大脑) down and stops it from yawn getting too hot, much like the fan in the computer. This might be why we're more likely to feel sleepy and yawn in warm temperatures.

What is clear is that we might yawn more when we're very tired and ready for a short sleep, and we can control ourselves when we do it. Yawning is something that we can't stop. It happens whether we want to or not. Once we start, nothing could stop us! It's also true that yawning is a contagious behavior. John Drury, a researcher from Sussex University, told BBC, "Dogs yawn when their owners yawn, and animals yawn to each other" His research of this behavior found that it is related to our social group and how close we are to these people, and that we are likely to copy their behavior.

Another research by the University of Nottingham in 2017 found similar results. They asked volunteers to watch other people yawn. They found people's ability to stop yawning was limited(限制) when others around them yawned. They also found when people were told not to yawn, or using electrical stimulation(电), their desire(欲望) to yawn would increase. These findings could be useful, the researchers said, because it might help treat other conditions like Tourette's(儿童抽动症), which involves the same area of the brain.

What is certain is that the act of yawning can happen at any time even when we think we're not tired.