The young actor who played Michel continuously mouthed Paulette's and others' lines. I had to rewind a few times to make sure I wasn't crazy. haha! He does it in several scenes. I still loved this film but that bothered me.
Let the world change you and you can change the world.
In the scene in question Paulette has just laid her head down face first on the floor so we can't see her lips move, we only hear her words. And, yes it appears that Michel is mouthing words.
Another theory is perhaps he was directed to say her lines in order that he would know when to say his own lines for the correct timing.