But mouths are a different story.
In the whole history of animation, there have been very few breakthrough substitutes for literal mouth shapes which is why the two Disney “inventions” described here are so interesting. In both cases, the Disney artists created original mouth constructions that can successfully smile, frown, and cry, but are not simple copies of the human equivalent.
A "trigger" is a visual cue that a particular expression is in progress, and it turns out that changes to the corners of the mouth are a very effective trigger for smiles, frowns, and crying. It seems quite likely that our perceptual apparatus is biased to assign much more weight to the mouth corners than the mouth middle, particularly with the closed mouth. As a result, this “trick” works like a charm – Donald is the world’s most popular cartoon character, but don't expect to use motion capture to animate a mouth this far from its human counterpart.
The second stylized mouth innovation revolves around teeth. For years, I taught that the display of reflective white teeth against the relative darkness of lips, mouth opening, and skin had evolved to help the open-mouth smile, and its opposite expression, the raised-lip snarl, be readable under all sorts of conditions. So, I thought that the top teeth being visable was critical to recognizing an open-mouthed smile. For example, just look at Aladdin's highly-expressive smile (at left). You can’t miss those pearly whites against Aladdin's darker mouth shape making his emotional state perfectly clear.
A less radical, but no less effective Disney mouth simplification is visible in Donald’s equally celebrated counterpart, Mickey Mouse. With surprising, but appealing, results, Mickey’s smile disposes of his teeth entirely. Never mind that the upper teeth ALWAYS show in an open-mouthed smile, Disney animators proved that the smile can be effectively read without any white display at all, provided that the signature "bow" shape is present. There seems no loss at all in clarity or intensity, and the world is equally smitten with the many toothless Disney characters who came after Mickey, like Bambi, Dumbo, and the seven Dwarfs.
Inspiration for Mickey Mouse's smile?