Deliberate mistake: One of Eva Marie Saint's lines in the dining car seduction scene was re-dubbed. She originally said, "I never make love on an empty stomach," but it was changed in post-production to "I never discuss love on an empty stomach." It is said that the censors felt the original version was too risqué.
North by Northwest (1959)
1 deliberate mistake - chronological order
Directed by: Alfred Hitchcock
Starring: James Mason, Cary Grant, Martin Landau, Eva Marie Saint
Factual error: When Cary Grant is attacked by the crop duster, he is supposed to be between Chicago and Indianapolis. Unfortunately, northwest Indiana looks nothing like this. The scene in the movie has miles and miles of treeless landscape. Even in the flattest farmlands of Indiana, there are many visible groves of trees.
[Roger Thornhill's matchbook carries the initials RoT.]
Eve Kendall: What does the O stand for?
Roger Thornhill: Oh, nothing.
Trivia: Alfred Hitchcock's cameo comes at the end of the opening credits. He can be seen missing the bus.
Question: Why do the kidnappers take Thornhill to the Townsend home and pretend to be Lester Townsend and members of his household? They could have taken him to some obscure place instead, at less risk of being found out.
Answer: More than likely, they felt that Roger would be dead and they would not be found out. The fact that he survives their DUI plot and returns to the house with the police only serves to makes him look more suspicious and guilty. It's to move the plot along, nothing more.
ChiChi
The bigger plot hole is, if Van Dam really believes Roger is Kaplan, why would he think that Roger would bring the police and go through the trouble of preparing "Mrs. Kaplan" to make the police think he's crazy? If Roger really was a spy, he doesn't need help from the police and would have just disappeared instead of retracing his steps. So if Van Dam anticipated the actions taken by Roger, he must believe at some level that Roger is telling the truth and would have looked deeper into it.