Yawning, as most of us probably already know, is as contagious as the common cold; in fact, just thinking about it right now might make you yawn. It happens to be an ancient, involuntary function panning across a huge number of animals, including humans, primates and even fishes, for that matter. So why is it that just thinking about yawning or looking at someone yawn makes us feel like yawning too? Humans, dogs, primates and almost all kinds of animals display contagious yawning. A yawn, or oscitation, is technically a reflexive action in which one simultaneously breathes in, stretches their eardrums and then exhales the breath. Yawning usually occurs before and after sleeping, or in the midst of tedious work. Although, yawning is considered to be associated with tiredness, stress, sleepiness, or even boredom and hunger; it most commonly occurs as a contagion when a person sees other people yawning.

The only concrete connection yawning being contagious has, is with age.

It has been found that the contagiousness of yawning decreases with age; moreover, children below the age of 4 years or children with autism do not display contagious yawning, although these children and adults will still display spontaneous yawning. In fact, babies start yawning by themselves by the time they're in the womb.