What I enjoy doing is rigging up all these animations and watching them work - up to a point at least. In the beginning of the video you can see the original cutout from the still image. After much time in photoshop I've re-painted pretty much everything so I have a lot of cutouts to use.
On the right what you see is the animation all being driven off of a single point, which is what I drag around to show you how it moves. There's quite a few really subtle things nobody would really think of until they have to actually animate one of these things. Such as when the nipple goes above the breast it has to re-draw the outer line, little details like that. Recreating just the breast is 7 layers.
Now you know! My plan is to release the .psd file and .aep file when I finish this one so other people can really play with it to see how it all works.