read someone's lips idiom
（尤指在无法听见别人说话时）从口型判断某人说的话，唇读，观唇辨意
to follow the movements of someone's lips in order to understand what is being said, especially if you are unable to hear them speak
She read his lips across the busy conference hall - "Time to go." 她在热闹的会议厅的另一端从他说话的口型判断他在说“该走了”。
See also: lip-read