A yawning is considered as a form of expression indicating boredom or a break in our train of thought. For many, it is relaxing or may occur in response to seeing someone else yawn. Nobody knows why one person yawning can cause others to yawn.
Scientists say that the question can also be asked of our primate relatives. They have presented evidence that yawns are contagious among monkeys, particularly with individuals of similar age and social status. This contagion is interpreted as a synchronization of activities ‘due to the imposition of wake-sleep rhythms on different individuals and to the attention they devote to each other’.
A yawning should be in a process of decreasing arousal according to them. If observed by other animals and if the observers arousal level becomes synchronized as a consequence the observers will also yawn. Accordingly, the yawn should be only a sufficient, not a necessary, factor in electing yawns from other group members.
Watching somebody taking a nap, in other words, might also induce a state of declining arousal and trigger yawns. One would expect observed yawns to be a more powerful stimulus, however, because another’s yawns might precipitate the observer attending to muscular tension in the facial muscles that can be dissipated by the yawn’s stretch. In addition one might expect observed stretches in general to be contagious, and yawns may thus be a particularly obvious example of the general behavioural synchrony of interact ants.