Your friend sitting across from you lets out a big yawn. What do you do?

Odds are you’ll yawn, too.

Scientists have discovered that yawning is “contagious.” Simply seeing a person yawn, reading about it or even hearing the word can trigger a yawn.

Humans yawn an average of four to six times a day, according to some research. But we aren’t the only ones who yawn. Animals, including dogs, cats, tigers and hippopotamuses, also yawn.

Contrary to a once popular belief, yawning is no longer thought to reflect a need for oxygen. Although the causes of yawning have not been proven, many experts theorize that it is a signal of boredom.

So the next time you feel overcome by inertia (see definition below), watch out! You may soon find yourself in the throes of boredom, and a yawn could quickly follow.

Speak your mind: What are the best ways to motivate yourself if you feel a spell of inertia?

INERTIA: A tendency to do nothing, inactivity, continue in its existing state.