Character mistake: In the scene when Gillian and Sally are dragging the boyfriend in to put him on the table Gillian says, "Watch his balls Sal". It is in Nicole Kidman's native Australian accent and the rest of the movie she speaks with a Northeastern US accent.
Character mistake: While listening to the fixed record at the antique music instrument shop, Chris talks about 1800 instead of 1900. (00:30:45)
Character mistake: At the beginning of the movie, Marnie states that she is 13 years old. When Grandma Aggie comes to visit, she tells Mom that it is Marnie's 13th Halloween. Since everyone celebrates their first Halloween before they turn one, if Marnie is 13 the events of this movie would occur on her 14th Halloween, meaning her powers would have faded by now.