People must have renounced, it seems to me, all natural intelligence to dare to advance that animals are but animated machines.... It appears to me, besides, that [such people] can never have observed with attention the character of animals, not to have distinguished among them the different voices of need, of suffering, of joy, of pain, of love, of anger, and of all their affections. It would be very strange that they should express so well what they could not feel.
~Voltaire, Traité sur la tolerance
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