Character mistake: After Spike comes out of the evolution device, he asks Iggy "Do you know what the square root of 26481 is?" And then answers "191". 191 squared is actually 36481. (00:47:20)
Character mistake: At the beginning Sally follows Jack at the end of the Halloween celebration where he sings "Jack's Lament." She then goes off to gather more deadly nightshade. Look at Sally when she sits down. It is in front of a stone labeled "witch hazel" and "deadly nightshade" is seen next to it on the right. Yet, Sally pulls two pieces of witch hazel out of the ground, before a quick cut back to the lab where we see her putting it in a jar marked "nightshade".
Character mistake: When Fish is offering Jack the contract to sell Henry to the Yankees, and later when Jack insults Henry's father, they both refer to Jack as Henry's manager. But Martinella is Henry's manager; Jack is Henry's agent. While the terms can be used interchangeably in other businesses, such as music, in baseball they are two separate titles with separate job descriptions.
Character mistake: Pretending to be a witch, April says that the song the walkman played was obtained because "I shrunk four incredibly cool guys and I locked them in there." The Barrio Boyzz were five at the song's release. Did she let one Barrio boy go? Was one of the Barrio Boyzz uncool? (00:16:40)
Character mistake: When Béatrice checks the historic book,Godefroy is born in 1076,but later in the film,Godefroy says that he's born in 1079.