Yawns were routinely preceded by rises in brain temperature. But once the outside temperature gets hotter than your brain, they found that there're a lot fewer yawns s. They also know that breathing through your nose tends to cool down the brain.
People yawn when they’re bored, right? So then why do athletes yawn before races? And why do so many animals yawn? … And why does reading this paragraph make you more likely to yawn?