Everybody yawns. Babies yawn, teenagers yawn in boring lessons, and even dogs, cats and fish seem to yawn. A yawn usually lasts only a few seconds: we open our mouths wide, take in a long breath, and then breathe out slowly. But why do we do it? The surprising answer is that scientists are still not sure.
For many years, people believed that we yawn because our bodies need more oxygen. However, in experiments, people who breathed extra oxygen did not yawn less. So today, most scientists think this explanation is probably wrong.
Another idea is that yawning helps to cool the brain. When we take in a deep breath of air, it may cool the blood that goes to the head. Some studies found that people yawn less on very hot days, when the outside air cannot cool them. This idea is interesting, but it still needs more research.
Scientists do agree about one strange fact: yawning is contagious. If you see, hear or even read about someone yawning, you are likely to start yawning too. In fact, you may be yawning right now! Why this happens is another mystery that researchers are still trying to solve.