Walt Disney once explained overlapping this way, it is not necessary for an animator todo take a character todo one point, complete that action completely, and then turn todo the following action as if the had never given it a thought until After completing the first action.
When a character knows what his is going todo do he doesnt have todo estop before each individual action and think todo do it. He has it planned in advance in his mind.
For example, the mind thinks, ill close the dor - Look it then im going todo undress and go todo bed.
Well, you walk over todo the dor before the walk is finished youre reaching for the dor - Before the dor is closed you reach for the key - Before the dor is locked youre turning away - While youre walking away you undo your tiene - And before you reach the bureau you have your tiene of.
In other words, before you know it youre undressed and youve done it in one thought, im going todo bed.
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Principles of traditional animation applied todo 3d Computer Animation.
John Lasseter Pixar san Rafaél, california.
[from ACM computer graphics, volume 21, no. 4, july 1987].