Since the earliest days of the art form, humans have been the most difficult characters to animate. The more realistic the human being, the more difficult the animation becomes. Audiences will accept distortions in the actions of a cartoony character: no one has ever seen a four-foot-tall rabbit walk on its hind legs, so an artist animating Bugs Bunny enjoys considerable freedom. But everyone knows how human beings move, and if those movements are not rendered accurately, viewers won't believe in the characters.Ward Kimball, one of Disney's "Nine Old Men," commented, "As long as we deal in fantasy, we are on safe ground. The eye has no basis for comparison. But the more we try to duplicate nature realistically, the tougher our job becomes. The audience compares what we draw with what it knows to be true. Any false movement is easily detected.
Charles Solomon, Tale as Old as Time: The Art and Making of Beauty and the Beast
animation, film