Sentence:  “So when we translate,” Lam was saying, “it's all about what we call <WSD>lip flaps</WSD>. Like, how many times does mouth move? We match translation more to mouth than to what words really mean. 
Meaning of the word marked with <WSD> tags:  A movement of an actor's lips, which is to be matched as closely as possible in a dubbed version of the film.