Hedgehog in the Fog

Today in class we watched Hedgehog in the Fog. I was fascinated with the way Norstein brought his characters to life. The motion seemed spot on and very smooth. I have not seen a film in a long time that left me with questions as to how they pulled it off. I'm curious as to how he was able to keep the characters' motion consistent while having the elements such as the fog remain undisturbed. I couldn't decide whether he shot this with an overhead camera leaving everything flat on a table, or if he had them upright. There was a scene where the hedgehog is laying on his back floating down a river. I wonder how Norstein was able to keep the water's appearance unaltered as he made the hedgehog's eyes blink, or allow the hedgehog to come into contact with water without ruining the puppet. I was thinking that perhaps he attached a stick to the puppet and had him a layer behind the river. There is also a giant tree whose bark looks very realistic. I'm not sure if he used a real tree or parts of bark to achieve that effect. The film overall was brilliantly done!