Revealing mistake: During the wedding scene, while the narrator is talking, you can see the string that will pull the left table apart. As said in the commentary, the filmmakers weren't going for the idea of people pulling the tables apart, but rather some other force parting them. (01:27:40)
Revealing mistake: When the Ogres guard the door during the coronation, Nish's club just brushes past his guard's face instead of hitting him in the side of his head.
Answer: He did in the film, but for the soundtrack she recorded the song with Jesse McCartney. In an interview he admitted to being a little nervous about the singing.