To be clear: they are not shadow puppets at all, they are not being displayed in the traditional way, but they are being captured with a camera.

In many scenes characters entirely change their shape in a natural or fluid way, because the cut-outs are being wholly replaced with different cut-outs from frame to frame, to simulate a natural/fluid motion. This is one of many techniques used in the film possible with stop-motion animation and impossible with shadowpuppets.

I watched the film and was quite impressed with the animation techniques used, although this isn't really novel but not because of puppets, animation actually goes back much further than film. It's a beautiful film though, and I can see why people preserved it.

https://www.theguardian.com/artanddesign/jonathanjonesblog/2...