Continuity: When the cop appears in the "Singin' in the Rain" dance number, Don is holding his umbrella with both hands, but in the next camera angle he holds it with one hand.
Anachronisms: As Kathy takes Don to Sunset and Camden, 1950s-era cars can be seen passing in the background.
Anachronisms: The Police Officer Don meets after singing the title song is seen wearing an oval L.A.P.D. badge. That design wasn't adopted by the L.A.P.D. until 1940 (the film being set in 1927).
Continuity: Cosmo's violin bow breaks and the hairs can be seen flapping about, yet when they finish the piece the bow is fixed.
Audio/visual unsynchronized: When Lena is having problems talking into the microphone hidden in the bush and Rosco and the sound man are in the booth, the sound man shakes his head and says, "She's gotta talk into the mike, I can't pick it up." His mouth clearly isn't moving as he says this.
Miscellaneous: During the Cyd Charisse nightclub dance number when she's wrapped around Gene Kelly, her body completely changes position between frames due to a clumsy edit. According to commentary on the special edition DVD, this cut of only a few frames duration dates back to the original release of the film and no one knows why it exists.
Continuity: When Don first meets Kathy and scares her, she shouts "Officer!" and points with her right arm. When we next see them pulling up by the road she is pointing with her left hand.
Revealing mistakes: The audience at the movie premiere at the beginning of the film is the same as the ones at the premiere of "The Dancing Cavalier" at the end of the film.
Continuity: In "Make 'Em Laugh", when Cosmo sits down on the couch with the mannequin, his hat is pulled down over his forehead and the brim is flat. In the close-up, however, his hat is pushed back and the brim tilted up.
Continuity: After the "Good Mornin'" number when all three are sitting on the upturned sofa, Cosmo and Kathy's sitting positions change.
Audio/visual unsynchronized: At the end when Kathy will sing "Singin' in the Rain" for Lena, Lena is asked "What key should the song be played in." She says "A-flat". The band leader says, "Singin' in the Rain in A-flat", and then proceeds to conduct the song in E-flat.
Continuity: During one of Don's stuntman acts, he goes into a building, and trees are blowing in the breeze. Right before the building blows up, the trees stop blowing.
Anachronisms: Several headlines from the popular entertainment newspaper "Variety" are shown, and Cosmo even makes a reference to "Variety". However, "Variety" did not publish its first issue until 1933 (the film is set in 1927).
Errors made by characters (possibly deliberate errors by the filmmakers): In Don Lockwood's film "The Royal Rascals" his character is seen pushing a man into a moat. Later when he jumps down to the same spot, it has become a cobblestone street.
Continuity: When the diction coach is reading 'Moses Supposes', O'Connor is making faces behind his back. When the coach catches him in the act, they both flinch. When the camera then cuts to a wider shot, you see them both clearly flinch again.
Miscellaneous: When R.F. Simpson plays the first talking picture demo at the after party of "The Dueling Cavaliers", the video is obviously edited in because as Mr. Simpson is walking off screen-right, the video cuts him off in a few frames.
Continuity: In the "Moses Supposes" scene, the book the Cosmo throws over his shoulder can clearly be seen to the left of the desk. By the end of the song, the book is gone and a miniature trash can has taken its place.
Continuity: When Don and Kathy are in the car together there is no windshield, but when she pulls up to R.F. Simpson's house there is a windshield. And when she leaves his house the windshield is noticebly larger.
Continuity: In the diction coach scene, the coach's arm changes positions between shots in a couple of places.
Continuity: During "Make 'Em Laugh", the green couch slowly changes position. It is in front of the hallway backdrop when Cosmo first enters that part of the scene, but it has moved stage left by the time Cosmo does the back flip off the backdrop.
Continuity: During Don Lockwood's voice training when Cosmo is making fun of the teacher, you can see the last "face" twice in different angles.
Revealing mistakes: When Kathy is singing for Lamont in the penultimate scene and the curtain is raised, at one point just before Cosmo enters the stage, Kathy fidgets and stops singing, but the voice can still be heard.
Crew or equipment visible: During the "Royal Rascal," when Don pushes the man over the railing on the stairway, you can clearly see the hands of a crew member reach out to catch him
Audio/visual unsynchronized: During "Moses Supposes", while Cosmo Brown (Donald O'Connor) & Don Lamont (Gene Kelly) are on the bench in front of the window wrapped in the striped draperies, Kelly's mouth movement to the lyrics gets out of sync.
Revealing mistakes: The scene where Gene Kelly is shown performing in an action sequence from the silent film "The Dueling Cavalier" actually uses footage from his earlier film The Three Musketeers (1948). At one point, Lana Turner, who played Lady de Winter in that film, is briefly seen coming through a door to embrace Kelly before being immediately replaced by new footage of Jean Hagen hugging Kelly.
Errors made by characters (possibly deliberate errors by the filmmakers): After the "Beautiful Girl" number, studio head R.F. Simpson (Millard Mitchell) discusses hiring Kathy Seldon (Debbie Reynolds) with Sid Phillips (Tommy Farrell) and Zelda Zanders (Rita Moreno). Sid Phillips delivers the line "Mr. Simpson might cast you as Zelda's sister." This is followed by an unusually prominent clicking mouth twitch, presumably out of character.