One of the UFO enthusiasts asks Monk "What's the frequency?" In a famous incident that Dan Rather reported, he was mugged by a man who kept asking, "What's the frequency, Kenneth?" This phrase is also the title of a song by the alternative-rock group R.E.M.
This was filmed in Piru, California, the same town as Mr. Monk Bumps His Head (2006)(4.11), & also the "Kick the Can" segment of Twilight Zone: The Movie (1983).
Tony Shalhoub starred in Galaxy Quest (1999), a movie about space travel and aliens much like the plot of this episode, as does Jeremy Howard, who plays "Bodysuit-wearing UFO Enthusiast" in this episode. And in this episode, people think Tony Shalhoob's character, Monk, is an alien disguised as a human. In Men in Black (1997), he really was.
Eric Stonestreet is the 3rd Modern Family (2009) guest star on this series. After Ariel Winter in Mr. Monk and the Astronaut (2006) and Julie Bowen in Mr. Monk and the Bully (2009).