I was reading Andreas Deja's blog post on dual character staging in animation when he posted this picture:
He said even though she's facing away from us, we understand through her body language and the juxtaposition of the concerned cat that she is sad/deep in thought.
It reminded me of something we learned in my evolutionary anthropology class in that learning to detect even minute, subtle cues in body language was an evolutionary adaptation for us to build complex culture, our species' killer app. It helped us build empathy and cooled our "wild nature". The ability to empathize with each other in effect domesticated us.
A lot of animation is so on-the-nose that I think we forget that our minds have evolved to be acutely aware of even the slightest hints of emotion through body posture. Acting has over time since the '50s gone from a more broad, theatrical style to an increasingly subtle reflection of our actual behavior.
Bouncy, obvious animation is fun to do and watch, but it shouldn't be at the cost of more subtle cues. Figuring out someone's emotional state is one instance where it's fun for the audience to meet the film maker/actor halfway. There couldn't be anything more natural for the viewer to do.