Ricardo is clearly standing on the dock as the ship pulls away, yet he turns up on board later as a stowaway.
The 3 uncredited, but identifiable actors playing the 3 aviators in their first scene, (Jay Eaton, Rolfe Sedan, Leo White) are not the same 3 uncredited actors playing the 3 sleeping aviators whose beards Harpo trims, but, in the next scene in which they appear, after their beards have been trimmed, the first three actors once again appear.
When Otis Driftwood arrives at his "suite" on the boat, the first time he enters, the room is small.
And in the next shots of the room, we see that the room is a little bigger.
The pipe that's in the room is closer to the back wall in the first version of the room, and more in the middle in the second version.
There's also a 2 light wall sconce in the big room that doesn't appear in the small one.
When Rosa is singing to Ricardo from the rail of the ship, she puts her handbag and gloves down on the rail to her left. In the next shot of her, they are gone.
When Otis Driftwood is sitting on top of the steamer trunk being pushed by the porter and has the porter stop in front of Rosa's cabin so he can go inside, he's wearing a hat. In the next shot, from inside Rosa's room as he enters it, he's not wearing a hat. When he leaves Rosa's room and goes to Mrs. Claypool's room he's still not wearing a hat, but after he leaves Mrs. Claypool's room and we cut to the next scene which is Driftwood entering his stateroom, he's wearing a hat again.
Lasspari is "abducted" from the stage as he is singing the famous "Di Quella Pira" aria from the opera "Il Trovatore". In the real opera, the hero sings the aria as he musters his followers to save his mother, whom he has just learned has been sentenced (offstage) by the Count di Luna to be burnt alive. In the film, he is singing the aria...to his mother.
Tomasso slips a violoncello part to "Take Me Out to the Ball Game" into the clarinet book for "Il Trovatore." A clarinetist would be unable to read, let alone play, a violoncello part.
The elevator operator uses the old movie trick of rising from a squatting position to make it appear that the car is rising from the ground floor. Unfortunately, the white elevator certificate over his left shoulder remains motionless the entire time.
During the overture to "Il Trovatore" when the orchestra members turn their pages and immediately launch into "Take Me Out to the Ball Game" you can see that their score consists of two pages of sheet music side by side. If they were really following it they should have continued playing the correct music from the opera on the left-hand page before they came upon the baseball anthem, which sits atop the right-hand page where Tomasso placed it earlier.
When Tomasso plays the harp, the sound is briefly out of sync a couple of times. This is due to the fact that Harpo Marx always recorded his harp music in a studio and then synched during the shoot.
When Tomasso is playing the harp, he is whistling. The fourth time he whistles, we hear his whistle but he doesn't move his mouth until about a second later.
During the Il Trovatore scenes, the extras' mouths are not singing the lyrics that are on the soundtrack.
Although Harpo may have actually played the harp on the soundtrack, he is only miming his performance on film. His fingers don't always sync with what's being heard, and some runs even happen while his fingers are at rest.
Shadow of camera and crane visible as Driftwood enters the rehearsal area and greets the singers.
During the contract scene, Baravelli makes a reference to the Dionne Quintuplets by saying to Driftwood, "Those five kids up in Canada." However, as they are in Italy at the time, he should have said, "Those five kids over in Canada."
Groucho, when Harpo is drinking one cup of water after another, says, "You know, they may have to build a dam in back of him." More reasonably, he should have said, ". . . in front of him."