A yawn is when the gap of the mouth extends and is followed by more rapid closure. For mammals or birds, a yawn happens when they take a long intake of breath and a shorter exhale follows the gaping of the mouth.

In other animals, including fish and snakes, there is no intake breath. The origin of yawning and what makes it happen is something scientists are still trying to discover.

To Yawn or Not To Yawn

Experts in the past believe that yawning removed bad air from the lungs. During the 17th and 18th century, doctors theorized that yawning would increase the oxygen in the blood, blood pressure, blood flow, and heart rate. Recently, health experts suggest that yawning cools down the brain, therefore when ambient conditions and temperature take place, yawning increases.

Scientists are still at odds with trying to uncover what makes a person have the need to yawn. When yawning occurs during social conflict and stress, researchers state that this is known as a displacement behavior. When a person yawns and their mouth is wide open, that can also be contagious.

Previous research states that people who are more empathetic tend to be more susceptible to contagious yawning.

Dogs Yawn Too

Researchers have tested if contagious yawning happens among dogs as well. In 2011, biologists from the United Kingdom examined 19 dogs. Only 5 dogs out of the 14 that were tested responded to an unfamiliar person's yawn. However, the researchers from the study couldn't prove the yawns were contagious.

Cognitive and behavioral scientists from the University of Tokyo tested contagious yawning among dogs while controlling stress. The researchers discovered that dogs were more likely to develop contagious yawning from a familiar person. The researchers also found that dogs can catch a yawn from humans and that yawning is considered to be a social behavior rather than a stress-related behavior.

A team of psychologists from the Unversity of Nebraska studied contagious yawning among shelter dogs in 2014. The psychologist discovered that a few dogs that yawned when a human yawned had elevated cortisol levels, which is also stress.

For the dogs that didn't yawn in response to human's yawning, the level of cortisol stress was not present in those dogs.

These findings state that certain dogs think human's yawning stressful and others don't. The researchers continued that more research is needed to confirm these findings.