The only parts that were actually scripted by Christopher Guest and Eugene Levy were the lines in the musical "Red, White and Blaine."
During the scene where Corky (Christopher Guest) is teaching the cast some dance moves, Eugene Levy can be seen in the back behind everyone, almost hidden from view. This is because whenever Guest would show off his moves, Levy would laugh so hard that they would have to cut and wait for him to stop laughing before doing another take. They figured it'd be best if Levy was in the back, where he would not be able to see Guest during this scene.
When playing Blaine Fabin in "Red, White and Blaine," it becomes necessary for Dr. Pearl (Eugene Levy) to remove his glasses. Unfortunately, Dr. Pearl's glasses corrected his lazy eye problem. Actor Fred Willard was unaware of the gag during shooting, and after delivering the line, "What did your keen and perceptive eyes behold?" to Fabin, stared at Levy's lazy eye, finally understood why his line was funny, and "was gone for about ten minutes" with laughter.
The musical auditions were the actors' very first public performances of their respective audition pieces.
Writer/director Christopher Guest spent a year and a half editing almost 60 hours of footage with editor Andy Blumenthal to come up with the final cut for the film.
Don Lake was originally cast as the principal of the high school who had problems with the rehearsals taking up the basketball team's floor. When the character was ultimately cut from the story, Lake was re-cast as the town historian. However, all the footage of him during the performance of "Red, White and Blaine", including his intermission interview, is of him as the principal.
The music and lyrics for "Red, White, and Blaine" were written and composed by Christopher Guest, Michael McKean, and Harry Shearer, who were the three stars of This Is Spinal Tap (1984).
The song "Nothing Ever Happens on Mars" was meant to be a complement to an earlier song in the show called "Nothing Ever Happens in Blaine," hence the audience's roar of laughter when the song starts.
Frances Fisher filmed scenes as Johnny Savage's mother but her scenes were deleted from the film. She does appear in the film's trailer.
Corky St. Clair (Christopher Guest) wears a Judy Tenuta T-shirt near the beginning of the film. Tenuta's self-given nickname is "The Love Goddess".
One of the collectible figures in Corky's shop at the end of the movie is Cliff Arquette in his Charley Weaver outfit. Cliff's son, Lewis Arquette, played Clifford Wooley, the narrator.