A dog, the body is dog's body; it must live as dog. But even a dog can be made a devotee. It doesn't matter. Because he has got the body of a dog it does not mean that he cannot be made a devotee. It can be trained. As you train the dog how to bite others at night, so you can train the dog also how to become devotee.
From Srila Prabhupada's lecture on Srimad-Bhagavatam 1.2.10 — April 24, 1974, Hyderabad