Other mistake: When Evie is in the library and all the book cases start to tumble over, if you look at one of the corner book cases you can see a piece of paper landing on it and the books are clearly painted on a flat piece of cardboard. (00:13:30)
Other mistake: Evie traces the marks on the inside of the coffin lid to show how they were made. Problem is, there are five parallel marks that all line up with each other. If they were really made be fingernails, the thumb mark would have been different from the finger marks. (00:56:20)
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? (01:23:10)
Suggested correction: This may be taking the dialog too literally. It may be foreshadowing, in the sense of "uh, oh, they've got us now" or Jonathan may simply be expressing the fact that he's had enough plagues now and would like it to stop please. By the way, you forgot the fire raining from the sky, so technically Imhotep did six, not five.
The fact that Evie stated specifically 10 plagues, it makes no sense for Jonathan to say "last" on the 6th one, without considering it a mistake on the parts of writers, actor, or director.
Jonathan doesn't simply say "last", but rather "last but not least" - a statement that is regularly used on things the speaker knows for a fact to be, in fact, not the actual last. Taken as a sarcastic remark it makes perfect sense in the situation.
I know he said more than just "last", but that was the keyword to point out that the mistake is in fact valid. "Last but not least", weather said sarcastically or not, is never meant to be said about something that is in fact not last. It's always said to indicate the last item is not necessary the least, such as at Christmas when the last gift remains or when the last graduating student is given his or her diploma.
Also it's a possibility that off screen there was death of livestock, lice, raining frogs and death of first born children. Just want to show which we missing and it's obvious why, as in a movie raining frogs or dying livestock isn't all that threatening to the main characters and doesn't look cool. And for the movie showing first born children die is just stupid. And lice, that's just too much like flies.
Other mistake: Despite nearly being hanged to death, Rick shows no sign of rope burns or bruising on his neck afterwards.
Other mistake: During the opening action scene, as Rick is firing the pistols after he backs up from the outer wall (shortly before he finds Beni and is locked outside the tomb), pay attention... you can see that many of the extras in the background aren't really doing much of anything even though the two groups are supposedly in battle. A lot of the raiders and doreign legion members are just standing around or aimlessly walking. Only a few of them are (poorly) pretending to "fight." (00:09:50)
Other mistake: At the hotel after the American has been relieved of his eyes and tongue and the motley crew realises the "waters" have turned to blood, Rick encounters Evelyn outside and behind her is a sign for "offices" that seems a bit too modern for the times.
