In a real life conversation, you don´t mantain your hands and head position like if you were a statue. If you are standing, you change the body weigh distribution from one feet to another every few seconds, and you don´t mantain your hands over your head in a unnatural position while you talk and talk, and talk... I think it would not take a lot of time of rendering to change a bit the stance of the body and members every image, and not only the facial expression of your interlocutor. It would give "life" to the characters and scenes. The devil is in the details, you know.