read (one's) lips
1. Literally, to interpret and understand what one says by observing the shapes of the words they form with their lips. Even though I was speaking very softly, Jill could read my lips and knew exactly what I was saying. I can read your lips, but it will help me if you use sign language as well.
2. To pay close attention and listen very carefully to what one says. Usually said as an imperative. A: "Come on, Mom—can I please go out with my friends?" B: "Read my lips—N O means no!" Read my lips—finish your dinner now, or you won't be getting any dessert!