Revealing mistake: When Imhotep transports Evie, Beni and himself back to Hamunaptra, Evie hears the plane and looks up. Before she states "O'Connell," you can see the letters and numbers on the side of the plane are backwards, like a mirror image - it says "B5538" backwards, which resembles "BE228" (no mirror). (01:32:15)
Revealing mistake: In the initial battle sequence, in one shot you can see the special effects canister from which the sand explodes up.
Revealing mistake: The first night after O'Connell goes back to Hamunaptra with Evie, the camp is attacked. In one shot, when O'Connell is shooting at the attackers, he fires and then swings the gun to his right and fires again. As he swings the gun around the flare from the gun follows the nozzle as though it were, say, a spark on a birthday cake sparkler, definitely not like the spark on a gun.
Revealing mistake: When Evie is chained to the altar next to Anck-Su-Namun, the closeup of Anck-Su-Namun shows the bandages across her throat twitching slightly with the actress's pulse. The problem is, she hasn't been brought back to life yet.
Revealing mistake: When the boat with the Medjai is heading towards the ferry, you see the one attach the hook to his wrist. You can see the bulge of his fist at the end of his sleeve, where he attaches the hook. If he was really without a hand, it would only be as thick as his wrist.
Revealing mistake: When the scarab beetles surround Benni at the end of the film, watch closely... you can see many scarab beetles running directly "through" each other, revealing they are just a digital effect. (This is also visible in other scenes with the beetles, but it's most obvious in this scene, particularly in the first shot when the beetles begin to swarm towards Benni).