你从不曾放声而笑那是因为我们不熟
[nĭ cóng bù céng fàng shēng ér xiào nèi shì yīn wéi wŏ men bù shú]
Translated to 'you never laugh aloud that's because we aren't familiar,' implies social awkwardness where laughter is reserved until there's sufficient rapport built up between both sides; stranger things are perceived through less open-hearted laughter compared with closer relationships.