Revealing mistake: When Carl is being dragged away by the demons, you can see the cable line that he's attached to. May be fixed on DVD.
Revealing mistake: At the beginning of the scene near the end of the movie with Lucius Malfoy fuming at Dumbledore in his office, Malfoy's hair is fanned back behind his shoulders. The lighting in the room illuminates the back of his neck, where you can see his real, short brown hair. (02:22:05)
Revealing mistake: When Anna and Hans are dancing in front of the lighthouse, we don't see the shadow of the railing or the ground they're standing on.
Revealing mistake: In the scene when the main character is in the library on the internet, she goes to a couple of websites. When the shot shows the URL up top, it is C:\windows98\mydocuments\etc.html. Instead of actually searching on the web they used a premade html page and accessed it from their computer.
Revealing mistake: After the woman is strangled and the people come in trying to find the little kid, the dead woman is clearly seen blinking. (00:11:25)
Revealing mistake: When Leo is laying his dead kids on the grass, the little girl keeps moving her eyes and breathing.
Revealing mistake: When Ace and Melissa are in bed together having sex if you look close enough you can see that she is wearing underwear. (00:45:35)
Revealing mistake: Right after Nell sends Hugh to hell, Dr. Marrow and Theo come out of hiding behind a pillar. As Marrow puts his hand on the pillar, it squishes in as if it was made of foam rubber, instead of stone. (01:39:50)
Revealing mistake: Before Paxton is hit with the 3 prong instrument, you can see the bloody holes already on his shirt. (01:01:20)
Revealing mistake: Gracie hugs the Russian waitress in order to have a better view of the disc hand-off appear on the monitor. As she raises her left hand that holds the book/camera lens, we see that the digital feed that appears on the monitor stays steady and level, even though she is raising the book/camera lens higher and closer to her face. Obviously the feed that we see on the monitor is not taken from the book/camera lens. (00:04:10)
Revealing mistake: In the shooting scene in the Mount Rushmore cafe, a boy in the background puts his fingers in his ears, because he knows the gun is about to be shot.
Revealing mistake: When all the kids are in the diner just before Chunk knocks over the water jug, Mikey starts to bang on the ground with a bar. When Brand stops him, Mikey calls him by his real name Josh. This is verified on the DVD by Sean Astin himself, in the commentary. (00:40:40)
Revealing mistake: When Loomis shoots the marshal's window out, when he makes a u-turn you can see the tire marks on the road and dirt from previous takes.
Revealing mistake: Most of the posed, fake displays in the ape's Museum of Natural History contain real people who are slightly moving if one pays careful attention. Especially noticeable are those posing with objects held in - or above - their hands.
Revealing mistake: As Drew Barrymore is running from the killer outside he stabs her. If you look closely it is very easy to tell it is a rubber knife, because you see it bend off of her. (00:10:20)
Revealing mistake: Throughout the film, the base station radio is not connected to an antenna. In many lengthy shots of the back of the radio we can see the power cord trailing out the back of the unit, but there is nothing plugged in to the antenna socket. This is especially annoying because base station radio problems are a key plot point.
Revealing mistake: At the end when Katie enters Hunter's room and throws Kristi against the camera, Katie's reflection in the wardrobe mirror shows her in a different position from when she attacks Kristi, to after she drops out of view.
Revealing mistake: After the sniper is shot he falls through the wall. Look at his silencer when he hits the ground - it bends where it attaches to the muzzle. A real metal silencer wouldn't do that. (00:41:25)
Revealing mistake: When the killer is attacking Cici on the balcony, you can see blood on Cici's back before she is even stabbed and both times she is stabbed, the knife that comes out of her back has no blood on it. (00:33:20)
Revealing mistake: When Ariadne is pulling the two huge mirrors close together underneath the bridge with Cobb, watch her when she is closing the second mirror. She steps over something even though there is nothing present for her to step over. There must have been a green screen frame there for her to step over.