Reading about yawning, hearing someone yawn, or even thinking about yawning can sometimes be enough to trigger one yourself.

It is called contagious yawning, and scientists still do not fully understand why it happens.

One possibility is that our brains automatically respond to the actions of people around us. Seeing or thinking about a yawn may activate brain networks involved in producing the same action, making the urge harder to resist.

Contagious yawning may also have a social purpose. Researchers have proposed that yawning together could have helped groups synchronize changes in alertness, activity or sleep, although the idea remains a hypothesis.

And humans aren't alone. Contagious yawning has been reported in several other animals, including chimpanzees, bonobos and dogs.

Interestingly, young children yawn from infancy but generally don't begin showing reliable contagious yawning until around four or five years old.

Still reading without yawning?