Well, from watching it, this is opinion, but here's what I think:
Belle isn't really Belle. First off, you can tell it's a voice over, and not her live speaking. Second, the hand motions are too much. It's a stand in. Third, there's no way it could be the actress who plays Belle, as two seconds later, she's in a big ol' yellow dress. Hidden underneath the cloak? Think not.
Moving on, the beast, he crouches over, and there is a lot of movement meant to be the beast speaking and so on, Belle, or the stand in, keeps all eyes on her, as the person playing the beast, slips out of the costume. That's what the movement really is. Carefully, the actor that plays the Beast slips into the wings, as barnum says, quickly pulls his clothes straight, fixes his shiny hair, and slips back into the Beast costume. (The whole time as the Beast in this scene, he is also dressed as the Prince beneath) Bing, Bang, Bada-Boom, throw away the Beast, and you've got your prince. Yay!