Continuity mistake: In the scene right before "Edelweiss", the Captain is asked by the children and Maria to play something on the guitar. The Captain is holding a glass in his right hand and then proceeds to raise his left hand in a negative gesture. The shot changes, and the glass is now in his left hand- with his right hand raised to gesture.
Continuity mistake: When Maria and the children are in a carriage riding around Salzburg, singing Do-Re-Mi, at one point (when she is sitting facing the kids) they pass a shop that is painted in a very distinct color and with a distinct sign (Frisor = a hairdresser) A few seconds later, as Maria turns around to sit forward in the carriage, they pass the same hairdresser.
Continuity mistake: Nicholas Hammond (Friedrich) was not a natural blond. The first scene to be shot involving him was the "My Favourite Things" scene and you can see that his hair is pale auburn. After this scene was shot, the directors thought that he would look better if his hair were lighter, so they applied an early form of bleaching agent to his hair. In scenes which were shot after this (notably the children's first entrance to meet Maria which occurs before the "Favourite Things" scene) his hair is very, VERY blond, almost white. In fact, if you scrutinise his hair closely throughout the film, it is a different colour in practically every scene, depending on when the scene was shot and how much of the bleaching agent had been applied.
Revealing mistake: When Gretl runs up to Uncle Max saying, "Can we really keep the puppet show, Uncle Max?", you can see Marta in the background begin her cue too soon as she starts to run up to Uncle Max in the middle of Gretl's line, but quickly stops herself. Then after Gretl finishes her line, Marta carries on and runs up to Uncle Max with the rest of the children and says her line.
Continuity mistake: Right after the boat tips over, the children change places between the first shot and the shot that shows them coming up out of the water. Most notably, Louisa moves from being over the left, in the front, to over the right and carrying Gretl out of the water. She doesn't have enough time to move back and pick up Gretl.
Continuity mistake: Part way through the "Do-Re-Mi" sequence, when Maria and the children are walking down the steps overlooking Salzburg, the sun changes direction. At first it's behind them, so their faces are in the shade. Then suddenly the light is in front of them, and their shadows have changed direction too.
Factual error: At his wedding, Captain Von Trapp is wearing three medium-width rank rings on the cuffs of his uniform (similar to a Commander in the Royal Navy and US Navy). In the Austro-Hungarian Navy, in which he served, this rank badge did not exist. Von Trapp actually held the rank of Korvettenkapitän (Lieutenant-Commander), indicated by one medium ring and one narrow ring. Even had he held the rank of Linienschiffskapitän (Captain), he would have worn one medium and three narrow rings. The only rank which had vaguely similar insignia to that in the film was Linienschiffsleutnant (Lieutenant), with three narrow rings. Even allowing for artistic licence re Von Trapp's actual rank, the insignia he is wearing simply did not exist.
Continuity mistake: Just before the Captain is about to sing Eidelweiss to the children, Max, Maria and the Baroness, the Baroness says to Max "Well why didn't you tell me, I could have brought along my harmonica." She has a glass of champagne in her hand and is about to take a sip but the camera cuts back to the Captain starting to sing and the glass is back resting in her hand. (01:21:30)