The professor noticed the students' constant clock-watching, clearly uninterested in the lecture.

clock-watching 是由名词 clock（钟表）和动词 watch（观看）组成的复合词，加上连字符构成名词形式。字面意思是"看钟表"，引申为"频繁看时间"的行为，通常暗示不耐烦或无聊等待的状态。