i beg to disagree. Audiences forgive a lot in animation. Now, if you obviously try, but do a poor job, that sticks out and they frown. But if you signal to the audience that you are not attempting to bring absolute verismilitude with a certain aspect of movement, such as highly subtle hand motion, they will not mind.

For goodness sake the (and I am NOT a fan) entire 'South Park" thing has NO body/arm motion, right?

So, the barest minimum is mouth movement. Not even full facial, but at least mouth.

It is not really a hot point, but my contention is that the first thing audiences expect is some sorth of mouth, then facial correspondence. I can not think of one case of animation with dialog where other movments were animated -- on a sliding scale of realism -- but no facial animation was attempted.

::::: Opera :::::