The increase of carbon dioxide in human blood stimulates the respiratory center of the brain, which is a physiological phenomenon. When yawning, unconsciously open your mouth and inhale deeply, then exhale. Chapter 3 of Ding Ling's Hu Wei: "He yawns from time to time. He lacks sleep too much. " Lao She's Four Generations under One roof: "He yawned for a long time, and the cool breeze and the cool moon seemed to enter his mouth together."
? Yawning and making sentences
1, the alarm clock at the bedside immediately rang. I opened my eyes in a daze, stretched myself, yawned, rolled on the bed a few times, and then got out of bed lazily, ready to wash.
When the baby stretched out his little hand and kicked his leg, yawned contentedly, and then opened his eyes, he happened to touch the first ray of warm sunshine in his life through the window and the birch forest in Siberia.
Every time in math class, every student can cheer up at first, but after half a class, students start to be distracted, yawn and so on. The math teacher put away his stomach full of scientific knowledge, took out his sense of humor and told the students a little joke. The students were amused, swept away their sleepiness and cheered up again.