Revealing mistake: As Harvey Dent is tied up in the warehouse with the explosive barrels talking to Rachel, if you look in the lower right hand corner of the screen, a green blanket on the floor moves up slightly as Harvey tries to get out of his restraints. It's too far away for Harvey to touch. A person's fingers or hand is also momentarily visible in the previous establishing shot when Dent is regaining consciousness.
Revealing mistake: When Batman's cycle flips the truck that the Joker is driving during the scene in which The Joker is attempting to kidnap Harvey Dent, the viewer can see the geyser of compressed air shooting from the underside of the 18-wheeler's trailer, which is commonly used to flip vehicles for movie stunts.
Revealing mistake: During the interrogation scene, when Gordon first enters, as he begins to close the door if you look in the glass reflection on Gordon's left (screen right), you can see the door open again slightly after he shuts it. In the next shot, its completely shut and locked.
Revealing mistake: In the opening scene, the Joker is picked up by some of the other crew members. While he is sitting in the SUV, he inserts a magazine into his Glock pistol and pulls back the slide to chamber a round. However, when he does, the slide locks back, indicating that the magazine is empty. (00:02:05)
Revealing mistake: In the scene where Batman is taking down the SWAT members to prevent them from harming the wrong people, one of the SWAT guys is lying on the ground and attempts to stand up. The clip for his gun contacts the ground and flexes like a rubber stunt gun would, not a real clip and gun.
Revealing mistake: When The Joker destroys the hospital the windows on the second and third story don't reflect anything. This is because the day before shooting at the abandoned building vandals broke in and destroyed the windows, meaning they needed to be replaced by CGI. Confirmed in the "Making of". (01:52:35)
Revealing mistake: In the scene after Batman thwarts the Joker's attempt to kidnap Harvey Dent by making the lorry the Joker is driving crash, the Joker crawls out of the lorry, picks up a gun and starts firing. In the background on the right alongside the Joker is a shop with the sign 'Sweet Home Chicago', where the scene was filmed - it should be Gotham. (01:18:35)
Revealing mistake: The Lamborghini Murcielago that Bruce Wayne drives changes from a real Lambo to a fake one - in the long shot (down an alleyway) showing the Lambo at the end of the street, It's obvious the wheel base is too short and the ride height is too high. It makes no sense why they would use the fake Lambo in this shot, as the car doesn't get damaged until later in the film. (01:46:00 - 01:51:00)
Revealing mistake: In the chase scene, the police helicopter appears to have NYPD markings instead of Gotham Police. (01:12:00)