Walt Disney once explained overlapping this way."it is not necessaryfor an animator lo 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 his is going to do he doesn't have to stop before each individual action and think to do it. He has it planned in advance in his mind. For example, the mind thinks, ' I'll close the door-lock it-then I'm going to undress and go to bed.' Well, you walk over to the door-before the walk is finished you're reachngfor the door-before the door is closed you reach for the key -before the door is locked you're turning away-while you're walking away you undo your tie-and before you reach the bureau you have your tie off.
In other words, before you know it you're undressed-and you've done it in one thought, ' i'm going to bed.'