"Sixteen Going On Seventeen" was shot in the gazebo, one of the last to be done. On the first take, Charmian Carr (Liesl) slipped while leaping across a bench, and fell through a pane of glass. Although she was not badly injured, her ankle was hurt and the scene was later shot with her leg wrapped and makeup covering the bandages.
Marni Nixon had become well known in Hollywood circles as a ghost singer for the leads in several film adaptations of hit Broadway musicals. She provided the vocals for Deborah Kerr in The King and I, Natalie Wood in West Side Story and Audrey Hepburn in My Fair Lady. "The Sound of Music" provided a rare onscreen performance by Marni Nixon, who plays Sister Sophia. Julie Andrews had previously appeared on Broadway in My Fair Lady but was passed over for the film. The producers were wary of how Julie Andrews would react to Nixon because she dubbed Audrey Hepburn's vocals in a role made famous by Andrews. When Andrews first met Nixon, she exclaimed, "Marni, I'm a fan of you!" and the producers were relieved.
Portia Nelson was the only member of the original Broadway cast to reprise her role in the film version.
Debbie Turner (Marta) had many loose teeth during filming. When they fell out, they were replaced with false teeth.
Nicholas Hammond (Friedrich) has brown hair, and had to undergo several painful hair bleachings before and during filming to make his hair blond.
Kym Karath (Gretl) couldn't swim, so the original idea was to get Julie Andrews to catch her when the boat tips up and they all fall in the water. However, during the second take the boat toppled over so that Andrews fell to one side and Karath fell to the other. Heather Menzies-Urich (Louisa) had to save her instead. Andrews stated later she felt guilty about this for years.
Kym Karath (Gretl) swallowed too much water upon falling out of the rowboat, and threw up on Heather Menzies-Urich (Louisa).
Duane Chase's (Kurt) high note in the "So Long, Farewell" number was actually sung by Darleen Carr (younger sister of Charmian Carr), as that note was beyond Chase's range.
Maria von Trapp: The elder of the two women in Austrian peasant garb who are in the background as Maria walks through a brick archway during "I Have Confidence".
Doris Day was apparently offered the role of Maria von Trapp, but turned it down.
Mary Martin was the wife of Richard Halliday, producer of the original Broadway show. Martin, who originated the role of Maria on Broadway, would eventually see nearly $8,000,000 from the film. In contrast, Julie Andrews earned just $225,000 for her performance.
Jeanette MacDonald was originally considered for the role of the Mother Abbess, and she was interested, but, in the end, her increasingly worsening health precluded her taking the part. She died a month before the film was released. Had she been able to accept, it would have been her first film in sixteen years.
Liza Minnelli, Patty Duke, Mia Farrow, Kim Darby, Lesley Ann Warren, Tisha Sterling, and Sharon Tate all auditioned/tested for the role of Liesl.
Julie Andrews nearly turned down the role of Maria Von Trapp, fearing the character was too similar to her role in Mary Poppins.
Julie Andrews was always Robert Wise's first choice to play Maria even though no one had really seen how she worked onscreen. Mary Poppins hadn't been released at that stage.
Christopher Plummer admitted that he ate and drank heavily during filming to drown out his unhappiness with making the picture, and found plenty of opportunities to do both in Austria. His costume eventually had to be refitted for his extra weight.
Christopher Plummer intensely disliked working on the film. He's been known to refer to it as "The Sound of Mucus" or "S&M" and likened working with Julie Andrews to "being hit over the head with a big Valentine's Day card, every day." Nontheless, he and Andrews have remained close friends ever since.
Christopher Plummer learned to play the guitar for his part, but the guitar (like his vocals) were re-dubbed.