Revealing mistake: In several scenes of the zombies swimming under water, they are obviously holding their breath. Would a dead zombie need to do that?
Revealing mistake: When Kate is telling the kids that their dad is quitting his job, the boy called Mike looks directly at the camera.
Revealing mistake: Dickie is in the garage with Sam and sally, and throws down the farm toy. You can see a battery on the ground, yet it is still making noise.
Revealing mistake: When Mrs Arness and her dog, William Shakespeare, are at Peter's house, the dog walks over to Georgie. You can see the actor who plays Georgie had to hold dog treats in both of his hands to keep the dog near him in the scene. Confirmed in the audio commentary. (01:09:05)
Revealing mistake: When Robert Downey Jr. is taking Halle Berry's blood pressure, the needle doesn't move as he pumps the hand inflator.
Revealing mistake: When Dae-su enters the room of one of his nemesis, his computer screen shows information about the stock exchange. The Internet address on the screen is: C:/DocumentsandSettings/[.]/OldBoy/[.], which would be a link to a folder on that computer, not an Internet address.
Revealing mistake: In one of the flashback scenes at the "bunker", a number of the shots fired pierce the sheet metal roof. When they show these holes, you can see fairly bright light coming through. This scene was supposed to be in the jungle during the night. There shouldn't be light streaming in; moonlight is not that bright. It was obviously artificial light used to enhance the scene.
Revealing mistake: After William Macy interviews Jeff Bridges and when the narrator is describing Seabiscuit's fans (the scenes are about an hour apart), you see shots of people in trees. They are the same shot.
Revealing mistake: When Martin Lawrence was trying to get into his car after he supposedly locked the keys in it, you can see in the shot from inside the car that the door was unlocked. You can tell because the orange-red sticker on the lock is showing, which wouldn't be visible if it was locked. (00:10:50)
Revealing mistake: When Watson is standing over Jackie's dead body and says "I'm sorry I wasn't there when you needed me most, my friend" you can see Jackie reflected in the TV standing ready for his queue before entering the picture. (00:41:55)
Revealing mistake: When the "light rail" vehicle is crossing the bridge, several shots reveal that it is not traveling on rails, but on a metal grating. This is most obvious after the police have stopped it. We see a bridge deck designed to carry cars & trucks (in fact, the police have just driven out on it) with strips of metal laid on the surface to simulate "rails". As others have observed, this was filmed on the wrong bridge; this makes it particularly obvious.
Revealing mistake: At the beginning when cutting the tomatoes onto the buns, Bob is not even coming close to the tomato in his hand, yet slices are falling off onto the buns. (00:03:50)
Revealing mistake: When Melanie, Tracy, Evie and Brady are in town, people can be seen stopping to watch the actors/look at the camera. (00:53:35)
Revealing mistake: During the cage fight, Su breaks a man's arm. We can see the break, however we can also see his real arm hidden under his shirt. There is a big lump under the fake arm. (01:01:30)
Revealing mistake: When young Ichi has a "climax" at the end, you can tell his "spunk" is really just white goop and isn't real.
Revealing mistake: The shots of the aircraft in flight (carrying the liver) at the beginning of the film have been flipped. The "tail number" of the plane is visible and is obviously backwards.
Revealing mistake: Katie Holmes appears to have a bandage on her finger way before she actually gets hurt. When Bobby hangs the turkey drawing on the door and she kisses him goodbye, the bandage is on her finger, but it's not until she peels the potatoes that her finger is cut. (00:14:25 - 00:24:50)
Revealing mistake: When Kathy is ripping open the plastic bag tied around Behrani, watch closely and you can see Behrani's eyelids flutter, although he's dead. (01:54:40)
Revealing mistake: When Selene notices the sword laying on the rocks, the sword moves up about two inches between shots, you can judge it by looking closely at the handle of the sword. (01:49:25)
Revealing mistake: At the end when the Monk With No Name has turned old and is walking away from Kar and Jade while waving to them (without looking back), you can see a finger on the left side of the screen covering up the corner and side of the lens. This is for sure in the wide-screen DVD version. (01:37:25)