Yawning cools the blood to refresh your brain

Researchers at the State University of New York in Albany found that yawning boosts blood flow and chills the brain. Vessels in the nasal cavity send cool blood to the brain during a yawn, making it operate more efficiently, said Dr Gordon Gallup, who led the study.

..."According to our hypothesis, rather than promoting sleep, yawning should antagonise sleep," he said.

The researchers also have an explanation for why yawns are so contagious...