I think these ladies are very interesting. There is a blonde and there is a brunette. Now note; The top half of the blonde is exactly the same shape as the top half of the brunette. AND, the bottom half of the blonde is exactly the same shape as the bottom half of the brunette. So why are they different? Because the top outline of one is joined to the mirror image of the bottom outline of the other. Or however you want to phrase it. Consequently, layers of blonds , each layer facing the opposite of the layer below and the layer above, will tile the plane. Layers of same-facing brunettes will tile the plane too. And layers, single or multiple, of either tiling can interlayer the other if the appropriate mirror image is chosen. Yes the anatomy is strained, but the exercise was fun.