The little authors didn't tag along today; it was just a simple meal, after all.
As they strolled out of the school gates, Shen Yuan let out a timely yawn.
"What's wrong? Didn't sleep well last night?"
Shen Yuan shook his head. "Yawning doesn't necessarily mean you're tired. The intense process of studying consumes a lot of energy in the nervous system, producing a large amount of carbon dioxide. When the carbon dioxide level in the blood is higher than normal, it stimulates the respiratory center, causing a deep breathing reflex—in other words, a yawn."
After listening, Li Zhi tilted her head. "Then why aren't *I* tired?"
"Hey, hey, hey! Are you indirectly calling me stupid?!" Shen Yuan shot her a mock-offended look.
"Well, you're not *that* stupid."
Shen Yuan blinked, feeling like he'd just been insulted again.
Walking down the street, the pair of Shen Yuan and Li Zhi naturally attracted a lot of attention.
