For this demo I used a character I created while I was on a trip to China for an animation festival. I got stuck in a seminar without an interpreter and didn't understand anything being said. Everyone was given some paper and a pencil, so, I just started drawing and out came this little bear character.

I started the animation with the keys and breakdowns.

Here's the initial pencil test.

These are the two key poses in opposition to each other:

And these are the two breakdowns in the passing position:

I then went back and inbetweened these and came up with this pencil test:

Lots of overlapping action going on here.

1) Obviously the arm swing which is based on the pendulum swing action,
2) The body action. Watch the upper torso. It has a form of the seaweed action in it - with more of a snap to it,
3) The head shape is overlapping as it moves up and down,
4) Watch the two tufts of hair on the top of his head,
5) Check out the ears.
6) Very subtle, but the toes overlap slightly with a bit of drag added in.

Most of this stuff is dealt with in the key poses and breakdown passing positions, but it really shows up in the inbetweening process. Most of the stuff is half way inbetweened, but some of it isn't, especially in the transition drawings between the "C" curve to "C" curve drawings - like on the arms at each end of the swing: in drawings 8 and 16 before the two keys and then 10 and 2 after the keys.