Scarlett's Hands - NOT a "Revealing Mistake"
If using someone other than Scarlett in the opening vegetable-cutting scene is a mistake, then so is using stunt drivers in a movie car-crash scene.
Directors routinely use hand models for closeups of chopping, writing, or any other hand actions. This avoids wasting the high-priced actor's time shooting a scene in which his or her face doesn't appear anyway. And it avoids production delays: if Scarlett isn't using the knife, she can't accidentally nick herself.