Why Do We Cover Our Mouths When We Yawn and Where Did the Practice Come From?

The yawn is now known to be the body’s way of infusing oxygen into a tired body, but suggestion is the only explanation for its contagiousness.

To ancient man, who had witnessed many lives leave bodies in a final breath, a yawn signaled that the soul was about to escape through the mouth and death might be prevented by covering it.

Because a yawn is contagious, the apology was for passing on the mortal danger to others.