Revealing mistake: When Jack and Rose are running from the raging water that is gushing down the hall after them you can see the faces of the stunt doubles through the computer generated ones of Leonardo and Kate (slow motion can help but isn't essential). (02:17:15)
Revealing mistake: When Holden is driving his Ford explorer, the speedometer reads that he's going 0 mph. (00:50:35)
Revealing mistake: At the beginning of the movie, when Melvin catches Simon's dog, he holds it away from him, with his arms stretched. When the dog begins to pee, you can see that the urine is coming out from Melvin's glove. (00:01:30)
Revealing mistake: The whole time during the president's escape from AF1 (the scene where he's fighting with his corrupt agent) you can see through the airplane door that there is a loop in the movement of the water. It moves for about a second, and then stops, etc., etc.
Revealing mistake: After Dante's Peak explodes for the final time, the pyroclastic cloud rolls down the mountain toward the town. Harry shouts "Don't look back, kids, don't look back." and then we are shown a wide shot of the truck zooming down the ash-choked streets. Unfortunately, it's painfully obvious that this is either a miniature or CGI shot, because the truck isn't leaving any tracks behind it or trailing any clouds of ash despite its high speed. (01:28:19)
Revealing mistake: In Dirk's first sex scene with Amber they are both supposed to be naked except for their shoes. At the end of the scene Amber sits up on the table on which they had sex as a female stage hand wraps her in a robe, and you can see she is wearing black panties.
Revealing mistake: When Garfield shoots an arrow at Cesar you can see stuffed padding under his sweater.
Revealing mistake: During the ending sequence, just as J.T. Walsh is pushing the truck on the bridge, there is a shot looking at the front of the semi and you can see that it is not J.T. Walsh driving. The stunt man is noticeably heavier than J.T. is, and his hair is messier.
Revealing mistake: When the monkey points up the hill and Odysseus keeps climbing, modern houses and roads are visible on the ground below.
Revealing mistake: Before Josh tells his mom about Buddy, Buddy starts to push the basketball with nose down the stairs. While he is doing this, you can see the treat put there just before the ball moves.
Revealing mistake: When they get Renn back into the room after he has been shot in the face with something acid-like, the smoke comes from behind his head. Not his face.
Revealing mistake: In the big speedboat scene near the end, when Cage is hanging off the side of the boat the stunt double is obvious in wide shots, where the entire boat is visible from above. He has big long sideburns, which are in stark contrast to Cage's short hair, visible in closer shots. At various other points in the movie, stunt doubles appear of much different physical builds than the two actors, with markedly different hair colours, and I seem to recall that at least one of them had facial hair.
Revealing mistake: As Mary Ann is dying, Kevin is holding her close to him, hugging her. From the behind shot of Mary Ann, you can see, sticking out from behind the right side of her neck/hair, is a tube and the yellow packet that held the blood/pump. (01:53:00)
Revealing mistake: When Ellie is traveling through space, she unbuckles herself from the chair to retrieve the compass. The chair then breaks off from the violent movements of the space pod, and slams up against the ceiling. At this moment, Ellie is in deep space in a completely weightless environment. She is floating, suspended in the pod and the chair itself floats a bit before being slammed upwards by the force of the pod movement. But, some small parts of the chair (bolts, etc.) are seen falling directly down, towards us in obvious full gravity; revealing that the scene was actually shot in normal gravity.
Revealing mistake: Towards the end of the film, a Cobra helicopter is flying in to assist with the extraction of the Navy Seals. There is a three-quarter frontal shot of the helicopter, one bank of rocket tubes can be seen to be empty; a few moments later, it's firing rockets from banks on both sides.
Revealing mistake: As Bobby drives along the dirt roads at the start of the film, in one shot when the camera is filming inside the car, you can clearly see the gear is in park position yet the car is "driving." (00:01:55)
Revealing mistake: When Matt Damon and Minnie Driver are sitting outdoors at Au Bon Pain in Harvard Square, Matt is telling her how he is able to "see" mathematical equations, just like Beethoven was able to "see" the notes on a piano. At one point during the conversation a girl wearing a red backpack (possibly a Harvard student) walks by in the background, stops and looks at the camera, smiles, and then continues on her way. (01:21:10)
Revealing mistake: When the partner-cop of Harrison Ford is killed there is shortly a scene where the dead guy is on the "table" at the hospital/morgue and you can see his jugular throbbing.
Revealing mistake: When the fireman goes to enter the fire truck that is on its side to rescue his friend, for whatever reason, the filmmakers sped up the film during his entry into the truck, it looks really out of place. (00:40:30)
Revealing mistake: When Jude Law needs to pull himself up the flight of stairs to reach the intercom, you can see him use his hips, despite the fact that he is paralyzed from the waist down.