Deliberate mistake: When Harry drops the Monster Book of Monsters, in the first shot facing Harry's feet as the book chomps at him, he runs backwards a few steps and he stands at the foot of the bed. However, in the shot facing the fireplace, there is actually plenty of floorspace now, much more than other shots, between the rug and bed for Harry to continue to run backwards. (00:15:15)
Deliberate mistake: In the scene where Frank and Jazira are trying to escape from the evil sheik, as they ride towards the gate to leave the town, the gate is closed and bolted, locking them in. The bolt is located on the outside of the gate, facing the desert, instead of inside the gate to protect the town.
Deliberate mistake: Polly's and Sky Captain's clothes are discarded because they are contaminated with uranium; however, Polly gets to keep her camera. Her camera would have been contaminated with uranium, too, because she had it with her in the underground cave.
Deliberate mistake: When Arthur follows Guinevere to the meeting with Merlin, her and the trees' shadows point at the viewer. Only Arthur has two shadows, one points to the left. The source of the moonlight is below the next ridge, and it's bright like a floodlight. Later, when Arthur is talking to Merlin, his face is always illuminated, even after a 180°-turn. (00:59:00)
Deliberate mistake: When Alexander is giving his pre-battle speech at Gaugamela, some of the shots are 'flipped', which has the odd effect of suddenly making all of the phalanx pikemen left-handed.
Deliberate mistake: In the scene near the beginning of the movie where Ben finds the pipe and finds the message by rolling the pipe on the paper, the message is long and has symbols, but it is impossible for all of that to fit in the pipe. (00:12:00)
Deliberate mistake: When the Neski file exchange takes place in the beginning, the Russian says "You can see who stole the money" and the camera shows the Russian documents. The documents (written in Russian), are in fact, a "Journal of Military Activity of Russian Army in April 1945." It is completely bogus and have nothing to do with the film. (00:07:15)
Deliberate mistake: In the first sequence, you see a man riding on the wooden battering-ram, and you can see where two different shots of the same man were spliced together, as the background suddenly shifts from being a forest, to being the exterior of the town, where the stone wall is. It was meant to be one single shot, but you can just see how the trick works. (00:00:30)
Deliberate mistake: When it starts raining so that "things couldn't be worse" according to Seth Green, the younger fat hillbilly pulls out an umbrella. Why would he have one when he is trying to hunt someone down and kill them? This was obviously put in for comedic purposes but doesn't play well in the movie. (01:05:40)