EDUCATIONAL TIP - Why Do We Yawn? Yawning is not just because you are sleepy. When you yawn, you take in a big breath of cool air. That cool air helps cool down your brain. Your brain works best when it is cool, not hot. So when you are tired, bored, or your brain is getting warm, you yawn to cool it down. That is also why yawning is contagious. When you see someone yawn, your brain thinks "I need cooling too" and copies them. You probably just yawned reading this. #chineduruby