Other mistake: Evie explains that if Imotep was resurrected he'd bring with him the ten plagues of Egypt. This is followed by (in no particular order) a plague of Locusts, Flies, Water running to blood, the sun being eclipsed and a plague of boils. At the plague of boils Jonathan says 'last but not least, my favourite plague - boils and sores'. How does he know this is the last plague? Aren't there supposed to be 5 more?
Other mistake: When Evie is walking around after messing up the library Jonathan scares her by making a mummy sit up. He then climbs out and says that he has something for her and moves the mummy's hand and arm about looking for the key. If you slow the film down when he's moving the arm you can see that it's just a piece of wood with some smaller pieces taped on the end.