The word for animal in Russian is животное. You will notice that it resembles the word живу ‘I live,’ and indeed the root жив- means ‘live.’ In fact in Old Russian the word живот meant life, although nowadays it means stomach. You'll note that животное has a neuter adjectival ending. I suspect that it originally was part of the phrase «животное существо» ‘living being,’ although that's just a guess. In any case, the word is now used as a noun, even though its endings are adjectival, and for that reason we can call it a deadjectival noun. It declines like this:

Notice particularly that since the word is neuter, the accusative singular does NOT copy the genitive singular.