Other mistake: When they are flying the dirigible through the night you can cleary see that there is a repeated pattern in the stars.
Continuity mistake: When Imhotep is talking to Alex O'Connell on the train through the black mask, his teeth are perfectly white and straight. A few seconds later, when Imhotep takes the mask off to show Alex, his teeth are like the mummy's - brown, green, jagged, and decayed.
Chosen answer: He says, "this just might work" meaning he and Alex trying to bring Evie back using the book of the dead.