What Happens When I Yawn?

Why Do People Yawn? Is It Because We Need Oxygen? Or Do We Yawn To Cool Off Our Brain? The Answer Is, Scientists Aren't Totally Sure Just Yet, But They Have Many Great Theories. The Vibrant Photographs And Diagrams In This Book Help Demonstrate What Happens In The Body When We Yawn. The Scientific Yet Accessible Text Was Designed To Both Interest And Enlighten Readers Of All Ages.