Continuity mistake: At the party Captain von Trapp puts on for the baroness, there is a scene where the guests are being greeted by Captain von Trapp and the Baroness inside the doorway of the house. When Herr Zeller is greeted and he looks ahead you can see a lady with brown hair in a pale blue dress being greeted in the background and then looking over her left shoulder. It then cuts to a scene where Herr Zeller has moved further into the house away from Captain von Trapp and the Baroness, and you can see she is greeted a second time and again looks over her left shoulder. (01:25:05)
Continuity mistake: When Maria leaves the Abbey to go to the Von Trapps, she walks for a ways, then takes what appears to be a rather long bus ride. This shows a fair amount of distance between the Von Trapps' house and the Abbey. Yet, when Maria snuck out to return to the Abbey during the party, it was night, and she had no ride waiting. Later, after the Captain tells the children he will marry the Baroness, they walk to and from the Abbey in an unsuccessful attempt to see Maria, and in an apparently short amount of time. From the initial bus ride, the Abbey was simply too far away for those walks to be believable.
Factual error: The story is set prior to the Anschluss, which was Austria's forced annexation with Germany in 1938. At this time Austrian vehicles still drove on the left (Hitler eventually changed that). When Von Trapp brings the Baroness to his home for the first time, he drives on the right.
Factual error: The von Trapp family's eating habits do not match the time and place. eg. They cut up all of the meat on the plate into bitesize pieces, then put down the knife, take the fork in the right hand and continue eating with only the fork. This would not have happened in an Austrian family of their rank at that time in history.
Factual error: When the Von Trapp family is hiding in the Abbey to avoid the Nazis, they are hiding behind some headstones. In reality, these headstones are flush against the wall and no one would be able to fit behind them.
Revealing mistake: In the Do-Re-Mi scene, when the children and Maria are running up and down the steps, Charmian Carr (Liesl) is doing the correct choreography, but was unsure of herself. Heather Menzies (Louisa) got it wrong, but did so confidently. Carr then takes a false step in order to make her movements match Menzies'. Carr confirms this in the 40th anniversary special: she second guessed herself during the filming, and that's why she corrected herself, but upon watching the movie, she realized she'd been correct in the first place. Viewers can confirm that Carr was correct because she initially lined up (diagonally) with the other children on her side, while Menzies was out of line.