眉头只是稍稍皱起却没理由
[méi tóu zhĭ shì shāo shāo zhòu qĭ què méi lĭ yóu]
'Just frown slightly, but for no reason' indicates the subtle mood change, maybe confusion or slight annoyance. It shows the emotional complexity and delicacy in one's daily life, like a gentle sorrow hard to explain clearly.