We do this every single day, at least few yawns before we get up from bed or before we go to sleep. We do this very often, so often that we became unconscious of doing it. So, before you continue reading, kindly remember how many times you yawn while reading this.
There was a theory about excess carbon dioxide. It was believed that if someone is not doing something or is tired, he/she breathes more slowly, and as breathing slows down, less oxygen makes it towards the lungs. And as carbon dioxide accumulates in the blood, an automatic response is then initiated, signaling the brain particularly the hypothalamus to send a signal to the lungs saying "Take a deep breath," and a yawn is produced. No wonder why we can see more people yawning in a boring classroom compared to people watching wrestling. But this theory was contradicted by some researchers Dr. Provine suggests that perhaps yawning is like stretching. Yawning and stretching increase blood pressure and heart rate and also flex muscles and joints. Evidence that yawning and stretching may be related comes from the observation that if you try to stifle or prevent a yawn by clenching your jaws shut, the yawn is somewhat "unsatisfying." For some reason, the stretching of jaw and face muscles is necessary for a good yawn. Just recently, researchers proposed that yawning is an act of cooling the brain. An experiment was done involving two groups of people, those who pressed warm or room temperature towel against their head, and the other group have it in a cold towel. It gave a quite impressive result. Those who had warm towels on their head yawned more often than those who had it cold.
By the way, how many times did you yawn? You forgot already? Me I yawned 3 times while writing this one. Interesting and unusual fact isn't it?
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