Woody is about to go from pose 1 to pose 2 - but not directly.

Here's a typical classic anticipation and overshoot.

Moving away from the start pose and then going past the end pose - then settling into the final pose gives the action more space. More space for the same amount of frames = a stronger accent. If the animator had just inbetweened the start and stop pose, the action would have had no impact. It'd be mushy.
http://www.cartoonthrills.org/blog/01Principles/antics/WoodySolidanticMad.movHere it is with every frame:
1) Start

2) Antic DOWN

3) Antic Right

4) one inbetween, arm overlapping the action

5) Overshoot (the furthest point in the action)

6) an inbetween and overlapping hair feathers

7) Final held pose - stop

Next: variations of antics
