Animal/Vegetable/Mineral?

Questions without answers riddles that rhyme

Animal, vegetable, mineral?
Isn't that how the game goes?
A simple question initially
and even quite superficially
But a dilemma just the same
Because I have seen stones
that do more than break bones,
and willows,
that do more than weep.
And men who are animals
without hearts that beat.

So who understands the difference
between one two and three?

Author's Note

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