Stop whatever you're doing, go to Seward Street and read through the James Baxter Animation Lecture. Here's a little snippet:
Muppets are James’ favorite example of acting with just the body. Without any facial expression they’re able to communicate the attitude.
In order of importance to James in animating a scene:
* 1. Body Language
* 2. Expression
* 3. Lip Sync
The body is the heaviest part of a character and therefore takes longer to change direction (see Inertia below). To try this out with your own body, move your head left to right 6 inches. Takes a relatively short time. Now try moving the same distance with your torso. Takes longer.
It’s not that heavier things move slower, just that it takes them longer to get up to speed. That’s what will make it look big. If you animate heavy objects slowly all the time, they’ll just look like they’re moving underwater.
In contrast, small characters take less time to accelerate and decelerate.