There are a number of quotes that you could use, depending on how you see the story. The nice thing about literature is that there's rarely just one answer.
Rainsford: Be a realist. The world is made up of two classes--the hunters and the huntees.
Whitney: I rather think they [the prey] understand one thing--fear. The fear of pain and the fear of death.
Zaroff--Life is for the strong, to be lived by the strong, and, if needs be, taken by the strong.