Revealing mistake: At the very start, as Anck Su Namun walks towards the camera, you can see two circular plasters underneath her body paint, preventing her from becoming too exposed. (00:01:20)
Revealing mistake: When Beni is in the tomb, the place is dark and is only lit by the candle he's carrying. However, when Beni turns around, his shadow on the ground doesn't change positions, indicating that it's not being cast by the candle, but by another source of light. (01:06:40)
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: Just after Rick shoots the sword out of Ardeth's hand, he flips over onto the ground to grab a stick of dynamite and quickly light the fuse. Look carefully, the fuse is already lit at the end and it doesn't even touch the fire.
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: In the first shot of the movie, the camera moves from the Sphinx through a town square. If you pay attention to the people in the crowd, it becomes painfully obvious which people are real (who were filmed in front of a green screen and composed into the scene) and which people are CGI. There's at least 4 (likely more) CGI people in the town square to populate it more, and they all noticeably move with a stiff, generic "walk-cycle" and even look slightly "blocky," like they're low-polygon models.
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).
Chosen answer: The tattoos on his forehead are the Egyptian Hieroglyphs that spell "Underworld", and the ones on his cheeks are the Egyptian Hieroglyphs for the word "truth." All Medjai males get these tattoos as part of the coming-of-age rite, when they turn sixteen, of which the most important is the tattoo on their right wrist (which Rick O'Connell also has) that marks them as "warriors for God." Other tattoos specific to Medjai males are on their arms, forearms, hands, pectorals, shoulder blades and beneath the navel - the tattoos on the nose and chin are no longer used, since the time of Seti I. Medjai females only get the wrist tattoo when they come of age, but are not marked with any of the other symbols that are particular to men. Fun fact: If the Medjai - male and female alike - shows any sign of pain or cries during the tattooing process, it is considered that they have brought shame to their family.