Don't Bug the Mosquitoes - S2-E12
Character mistake: When the "Honey Bees" (Mary Ann, Ginger, Mrs. Howell) perform, Mrs. Howell (Natalie Schafer) messes up her lip-syncing throughout the number. But it is most noticeable at the very end when the girls put their heads together and say "buzzzzzzzzzzz" but Mrs. Howell is mouthing an "oooooooooo" which she changes to a "zzzzz" mid-way through the note.
Adam, Warlock or Washout? - S8-E14
Character mistake: In Season 3, Witches and Warlocks are My Favorite Things, Maurice says he won't stay for Tabitha's testing coven because it's "women's work" but in this episode, when Adam is finally tested, he arrives and says he wouldn't miss seeing his grandchild being tested.