Yawning is contagious. Even thinking about yawning is enough. In fact, there's a 50% that you're about to, or just did, yawn.
Yawning is a reflex of simultaneous inhalation of air and stretching the ear drums followed by an exhalation of breath. It is linked to tiredness, boredom, overwork, stress and lack of stimulation. In humans, yawning is often triggered by others yawning around you.
In this way, it is contagious. Interestingly enough, this contagiousness has also been observed in chimpanzees and dogs. So why is that when we see those around us yawning, we too want to yawn?
Some studies have suggested that infectious yawning developed to keep groups of animals alert. The increase of oxygen to their brain will help ready them for action. Other studies have suggested that yawning is associated with the cooling of the brain.