上课铃就是催眠曲下课铃才是最强音
[shàng kè líng jiù shì cuī mián qŭ xià kè líng cái shì zuì qiáng yīn]
'The bell for class is a lullaby; the after-class bell is the most appealing sound.' This expresses that some students find classes boring, hence treat them like something dull, and instead look forward to the end of classes.