The original stage version of Maria’s song “I Feel Pretty” included the lyrics “I feel pretty and witty and bright / And I pity / Any girl who isn’t me tonight.” In the film of West Side Story, this night scene was changed to the daytime, and presumably for this reason, the rhyming words “bright” and “tonight” were changed to “gay” and “today.”
Throughout the movie, Natalie Wood wears a bracelet on her left wrist, not for any aesthetic reason, but because she had injured her wrist in the scene of The Green Promise (1949) when she fell on the bridge that collapsed during the severe rainstorm, causing an unsightly bone protrusion on her wrist. She wore the bracelet to hide the injury. It became her trademark in all of her movies.
With its win of 10 Academy Awards, this became the biggest Oscar-winning musical of all time, beating the record Gigi (1958) set three years before with its nine Oscars.
West Side Story was the first film to win a Best Director Oscar for two directors , Robert Wise and Jerome Robbins. Wise directed the drama while Robbins would handle the singing and dancing sequences. Robbins developed a habit of shooting numerous takes of each scene, to the point where the film went over budget and behind schedule. He completed four numbers – the Prologue, “Cool”, “I Feel Pretty” and “America” – before he was removed from the project. – IMDB
Natalie Wood’s singing was dubbed by Marni Nixon, one of Hollywood’s most celebrated playback singers. She dubbed Marilyn Monroe’s high notes in Diamonds Are a Girl’s Best Friend from Gentlemen Prefer Blondes and worked closely with Deborah Kerr to supply the star’s singing voice for Rodgers & Hammerstein’s The King and I. For West Side Story, the studio kept her work on the film a secret from Natalie Wood, and Nixon also dubbed Rita Moreno’s singing in the film’s “Tonight” quintet. She sang Wood’s high notes in Gypsy. For My Fair Lady, she worked with Audrey Hepburn to perform the songs of Hepburn’s character Eliza Doolittle. Because of her uncredited dubbing work in these films, Time magazine called her “The Ghostess with the Mostest”. – Edited from Wikipedia