Koschei is, if you will, a dishonest bogatyr (a hero-knight from East Slavic folklore). He possesses all the qualities and attributes typical of a bogatyr, such as an enchanted sword and a magical horse, but unlike other bogatyrs, Koschei cannot be defeated in fair combat, because his death has been removed from his body and hidden—usually at the tip of a needle, the needle in an egg, the egg in a duck, the duck in a hare, the hare in a chest, and the chest in an oak tree. Variations are possible. In some tales, the egg is hidden in a fish, but fundamentally, in our view, a fish is no different from a duck. http://www.vedomosti.ru/newspaper/article.shtml?2007/11/23/136655
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