Yawning

Three things are sure to make the majority of us yawn. Yawning due to fatigue, boredom, or witnessing another person yawn. The first two seem to be connected in some way, and the third is just that sneaky, contagious yawn that no one likes. But, it's important to note that yawning makes no sense biologically, regardless of what is happening when you begin to yawn.

Yawning is a characteristic that both humans and animals share, and while it does sometimes signify fatigue, the exact reason why is unknown. Why would this wide-mouthed expression be used to express fatigue?A confounding side effect of a gesture that denotes tiredness is that yawning causes hormones to briefly boost heart rate, which provides a tiny pick-me-up when you're tired. The fact you yawn when you wake up as well as when you're ready for sleep makes this all the more puzzling. So far, it has not been possible to determine what a yawn actually does.