Visible crew/equipment: When Professor Higgins is having Eliza practice saying the letter H by blowing into a tube to make the flame waver, the paper she's holding is actually Rex Harrison's lines. Once the paper starts to burn and the camera angle changes, you can read them and it's practically all of his lines for the whole scene.
My Fair Lady (1964)
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Directed by: George Cukor
Starring: Audrey Hepburn, Rex Harrison, Wilfrid Hyde-White, Stanley Holloway
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More mistakes in My Fair Lady
Eliza Doolittle: I ain't dirty! I washed my face and hands before I come, I did.
Trivia: Rex Harrisson also played Henry Higgins on broadway. He wanted Julie Andrews for Eliza as well, since she had also played Eliza on broadway. (Julie didn't get the role obviously, but did play Mary Poppins that year, and won the Best Actress Oscar).
Question: Why would Zoltan Karpathy think that Audrey Hepburn is "born Hungarian, possibly of royal birth" when her name is Eliza Doolittle?
Answer: He knows that Professor Higgins is trying to pull a fast one by having Eliza pretend to be someone else, and he fancies himself as much of a linguistic expert as Higgins. He's correct that there's something going on; he just gets the wrong end of the stick and assumes she's "high born," thus proving Higgins right that he could "train" Eliza to pass as upper class.