through is the movement that happens after the actual action. This
makes sense when you think about the conservation of momentum. If
you throw a ball your hand would gain speed, since your hand has mass
it wants to keep going (Newton's First law). This is the follow
Follow through also helps to define the mass of something if it
is light it can slow down very quickly. But if it is something large
it will move slowly and slow down slowly. If two objects are moving
at the same speed the larger one will travel farther unless more force
is applied to slow it down.
If there is a large dinosaur in an animation it is going to make
slower changes in movement; where as if there is a small bird it can
hop from point A to B to C in a blink of an eye. The follow through
action can almost be disregarded with some thing small such as a bird
and no one would comment about it. If you ignore the follow through
on something large, people will notice. They may not know why, but
they will say that it just didn't move right.
Overlapping Action is something else used to make things look real.
Overlaping Action is the starting of a new action before the previous
one was finished.
Walt Disney explained it best in this quote: "It's is not necessary for an animator to take a character to
one point, complete that action completely, and then turn to the following
action as if he had never given it a thought until after completing
the first action. When a character knows what he is going to do he
doesn't have to stop before each individual action and think
to do it. He has it planed in advance in his mind."