有两颗心叫心照不宣有两个人叫形影不离
[yŏu liăng kē xīn jiào xīn zhào bù xuān yŏu liăng gè rén jiào xíng yĭng bù lí]
Expressing deep mutual understanding ('unspoken understanding') and inseparability between two people ('inseparable as shadows'). This signifies the unique and profound connection shared by two individuals who always stand by each other without needing words.