Plot hole: The incantation for Magicae Maxima must be repeated 7 times without making a mistake, or they have to start over. Winnie says the spell wrong but the spell works anyways. The first time she says it (with Book), Winnie says "From North, the East, the South, the West," but the last time she says it (without Book), she says "From North, South, East and West" (not in the right order).
Plot hole: The spell Magicae Maxima works, but it shouldn't have worked at all because there was one ingredient missing, the petrified spider.
Suggested correction: The spell works because Winifred believes it is a petrified spider. It also works because she believes that Billy Butcherson was her lover; which he wasn't, as stated several times in the movie: in the flashback scene, Billy mentions it several times to Gilbert, and especially when Sarah tells Winifred that Billy was her (Sarah's) lover, to which Winifred replies that Sarah was just a fling; so the spell can work with incorrect material as long as Winifred, as the main witch, believes it.
