I notice this one every time I read the book, and it really bugs me. In the beginning of the book, it says that Munroe's last name is Jaffray, and then there's Grandfather Jaffray or whatever his name is, and so on. Then, further into the book, suddenly he's Munroe Jaffrey, and Grandfather Jaffrey. Then it switches back to Jaffray. This is a pretty glaring slip-up, if you ask me!