Audio problem: When Otto is being run over by the steam roller at the airport, he starts screaming as he is being run over and when the camera angle changes you can still hear him screaming but the stuntman's lips aren't moving as the steam roller goes over him and he's sinking into the wet cement. (01:43:00)
Continuity mistake: When the steamroller is going over Otto, you can plainly see that the cement is still very wet and loose, but only moments ago Otto's feet were stuck in the cement because it was hard and thick. (01:43:01)
Continuity mistake: Right after Ken runs over Otto in the steamroller, Archie starts running away and in the background you see the steamroller being put into reverse. The camera angle changes to a closeup of Ken and the steamroller is going forward. (01:43:09)
Continuity mistake: As the plane is taking off, Otto is trying to hang on but the wind pushes him off. The camera angle changes to a wide shot of the plane taking off, and Otto is not seen anywhere but you still hear him screaming. (01:44:30)
Continuity mistake: After Ken reverses the steamroller after running Otto over with it, you can see a red patch signifying his splattered body in front of the roller. However, a few scenes later, Otto is seen alive. (Otto was originally meant to die, until test audience feedback influenced a change of mind on the part of the filmmakers.)
Continuity mistake: Otto stabs a knife into the baby seal poster. Several shots later, the poster is undamaged.
Revealing mistake: During the trial, George calls Wanda a b*tch and runs towards her, jumping on the tables. The actor is replaced by a very obvious stuntman: younger, with a fuller moustache, and with longer and darker hair.
Continuity mistake: Ken is trying to kill the witness and crashes his car against a garbage container. The garbage swaps from being on the center of the hood to on the left side depending on the angle.
Continuity mistake: When Wanda arrives at Archie's office, there are piles of papers/books on the mantel beside the door, stacks of papers/books, a lamp and draperies behind Archie. During Wanda's visit, things behind Archie change, disappear, then reappear, the lamp changes the direction it points, the draperies change, and part of the piles on the mantel change entirely.
Revealing mistake: Towards the end when Archie is driving Wanda to the flat in his car, during the shot when she asks him to "say something in Italian" you can see John Cleese is trying desperately hard to keep a straight face (and not altogether succeeding).
Answer: John Cleese was reciting the poem "Molitva" by Mikhail Lermontov. He learned and memorized it phonetically and has admitted that he had no idea what the words actually meant.
Angela Brown