Brüderchen und Schwesterchen

Two poor orphans fled from the evil stepmother into the forest, but the boy got very thirsty and wanted to drink from a spring. But these were all cursed, in that he was always supposed to turn into a different animal as soon as he drank from them. He was so thirsty that he couldn't help himself and drank from the spring, which turned him into a deer. So he lived with his sister in the forest until the king organised a hunt there....

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Image source: Kurenai