One theory is that by moving the muscles in the face and neck, yawning stimulates the carotid arteries in the neck, increasing blood flow to the brain and waking it up. Additionally, a 2012 study ...

The exact causes of contagious yawning are still debated, but two leading hypotheses are the nonconscious mimicry hypothesis ...

An curved arrow pointing right. Have you noticed the domino effect that occurs when someone in the room lets out an unnecessarily long yawn? Well, there's a reason why yawning is so contagious.