Maybe he means you can describe each person as an animal according to his or her personality. People with strong personality can be easily associated with some kind of animal, so this advice basically guides you to hire an interesting group of people.
One of the best tricks I learned during our startup was a rule for deciding who to hire. Could you describe the person as an animal? It might be hard to translate that into another language, but I think everyone in the US knows what it means. It means someone who takes their work a little too seriously; someone who does what they do so well that they pass right through professional and cross over into obsessive.