Errors made by characters (possibly deliberate errors by the filmmakers): In the scene where Glinda appears in Munchkinland and meets Dorothy, she asks Dorothy whether she is a "good witch or a bad witch". Seconds later, when Dorothy learns that Glinda herself is a witch and comments on her beauty ("I've never heard of a beautiful witch before"), Glinda replies with "Only bad witches are ugly", a statement from which she herself should have been able to deduce Dorothy's morality (good or bad).
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