Yawn

 Yawning (oscitation) is most commonly experienced in adults immediately prior to and after sleeping, during tedious activities and as a result of its infectious quality. It is usually associated with tiredness, stress, sleepiness, boredom, and even hunger. For humans, yawning is usually triggered by the impression that other people are yawning (for example, seeing someone yawning, or talking to one on the phone that is yawning). This is a form of positive feedback. The "contagious" behavior of yawning may also be observed in cats, dogs as well as birds. It is even observed across species. Scientists have identified about twenty psychological causes for the yawning phenomenon, however, they are not all the same. The sound can be observed in chimpanzees cats, dogs, birds, and reptiles. In humans and animals the act of yawning may be associated with the natural instinct to stretch different parts of the body such as the shoulders, neck, and the back.