At the beginning of the episode, Trivette is reading from a book while he and Walker are on a stakeout. Walker asked the name and author of the book. Trivette says "The Secret Power Within by Chuck Norris". Walker says "Never heard of him." Trivett says "You've never heard of Chuck Norris, four time World Karate Champion?". Walker says "Six"
Chuck Norris, who stars as Walker on this show, is mentioned during a conversation about "The Secret Power Within", a book that Norris himself has written. This reveals that Norris also exists in the show's fictional universe.