Factual error: The filibuster scene gives the impression that the Senators were powerless to stop Jefferson Smith's speech. However, they can make a speaker shut up if at least 3/5 of the Senators vote to. From the Senators' reactions, a lot of them probably would have voted to silence Smith. (Clearly, if this had happened, the movie would be much less interesting).
Revealing mistake: When a car drives by a store front and two hand grenades are thrown at it, the hand grenades bounce back into the street before the store blows up.
Revealing mistake: When we see a wagon with a woman and several children in it, the horses get spooked and run. A woman is seen desperately trying to stop the runaway horses. In the next scene you can see the children are not real and the woman is a man dressed in a woman's dress, obviously a stunt man used for that scene.keiko
Factual error: When Cagney surprises Ward Bond in a saloon, they run out the back and across a rail freight yard. They jump onto boxcars of a slow moving train. Bond jumps up between two older wooden-bodied boxcars, A and B. Cagney, in pursuit, jumps up between cars B and C. In the wide shots, car C is seen to be a steel-bodied boxcar built at the earliest in the late 1930's. Events in the movie show the time-line to be set in September, 1893.tcmfan43
Factual error: Towards the beginning of the film, when Kitchener is shown inspecting Harry's old regiment, one of the African or Egyptian troops is shown to be wearing the Pattern 1914 Infantry Equipment, not made until 1914 at the earliest. Additionally, it has the 1918 modification to have two closing straps, so is over 20 years too late for the 1894 date at that point.Andrew Upton
Continuity mistake: When the dog in the audience has his feet crushed by the hippopotamus sitting down on his chair, you can see that there is an empty chair next to the dog, but in the next shot the chair has disappeared.
Character mistake: On the proclamation announcing a plebiscite on a proposed "monarchy", the adjective "monarchical" is misspelled "monarchial".
Continuity mistake: During the Blue Birds in the Moonlight song you can see Gulliver holding his drink. In the next shot while he's laughing the drink has disappeared.