Deliberate mistake: Practically all movies incorporate the name of the movie within the dialog. However, they must remember the English language and tense agreement. On at least two occasions, Fishburne says "Come on Dodge, lets FLED." If they were so interested in incorporating the name within the script, they should have named the movie FLEE.
Deliberate mistake: In the prom scene at the end, there is a shot of a couple dancing with his hand on her rear-end. A counselor comes over and hits the boy's hand to make him move it. He complies, they kiss, and he puts his hand back when the counselor leaves. The camera cuts away to a different shot, and then returns to an over-head wide shot of the crowd. Down in the lower left-hand corner you can see the exact scene with the couple and counselor being filmed.
Deliberate mistake: In the end of the NASCAR race, Tripp and Gordon get into a crash making Gordon spin, but he somehow is still able to come in second place even though every other racer was right on his back when he spun. He wouldn't have been able to regain that much speed in that short amount of time.
Deliberate mistake: When Carrie is hiding in the locker room to record John talking with his friends, it's clear that her camera is behind the vent, and the openings in the vent are closer together then the diameter of her camera lens, however we don't see the vent slats in the camera view or the replaying of the video footage in a later scene. Not to mention the fact that she isn't holding the camera steady. This is impossible.
Deliberate mistake: In the scene where Forrest is describing his heritage, the clip of KKK on horses is taken from The Birth of a Nation. In this clip, you can see tire tracks on the dirt road well before automobiles were supposed to be in existence. Robert Zemeckis decided to leave this mistake in to perfectly match the clip to the original movie.
Deliberate mistake: This was probably done intentionally to make them more visible, but the bullet holes left in the stairwell wall by Bart's handgun while he is chasing Danny during the movie's climax look to be about the size of golf balls. Typical handgun calibers aside, just looking at the size of the clip he's loading into the gun and seeing how many rounds it holds, those rounds would have to be much smaller than the holes the bullets made.
Suggested correction: It's a 9mm Glock18. The standard magazines have 17 rounds, the long ones 30. The holes could be larger because it's an old building and the plaster might break apart differently than modern drywall.
Deliberate mistake: During the chariot race, the chariots crash together but the arrangement of the horses make it impossible for them to actually collide. In some instances (particularly in an aerial shot as Ben Hur and Messala round the turn) it is obvious that they repositioned the shaft of the chariot to between the first and third horses instead of being in the centre between the second and third.
Deliberate mistake: The car Rudy, the mechanic, is working on is a 1971-72 Plymouth (the one where the chassis falls down around him). Plymouth's of that era were unibodies, which means that the body and the chassis were all one piece and not separate, so there's no way a chassis could have fallen down like that from that particular car, since it didn't have a separate chassis.
Deliberate mistake: When Prince Hapi says that Monique should be his seventh wife, she says "you have seven wives?" and he confirms. Actually if she is supposed to be his seventh wife he only has got six wives by now.
Deliberate mistake: When Tiff (as a doll) lights her Zippo you don't see her clicking the flint, even though one can hear a 'clicking' sound. (00:33:35)
Deliberate mistake: When Tom Hanks is picked up at the airport by a taxi, its license plate number is TX7943. Later when he is picked up at the Ramada Inn, he is picked up by a taxi with a different driver, different numbers on the top, but has the same license plate number.
Deliberate mistake: With John Cusack leaning to the side to pull Diane Lane and the dog from the water, the rowing scull should have nearly tipped over, yet it leans only slightly. Later in the same scene, the normal instability of such boats can be seen when tipping occurs to a greater degree simply from the dog moving.
Deliberate mistake: Frankie's voice-over reading of the letter to his father does not match the text of the letter. He says, "Ricky Munroe told me. Trust him to put his big feet right in it. I've told him hundreds and hundreds of times." but the letter reads, "Ricky Munroe told me. Trust him to put his size threes right in it. He is rubbish at secrets. I've told him hundreds and hundreds of times." (00:21:15)
Deliberate mistake: The tiny hot air balloon that Francesca released in the debate room would never be able to support Casanova's weight.
Deliberate mistake: In Antarctica when Charlie and Cam kiss, their tongues become froze together but this is impossible as it would take a freezing object for this to work.
Deliberate mistake: Walter slips on a golf ball in the judge's bedroom and the stuntman is seen taking the hard fall. (01:19:05)
Deliberate mistake: After Ashley gets covered in mud, for the next five minutes or so of the movie the amount of mud on her constantly changes between shots, especially on the back of her head.
Deliberate mistake: During the dance number in the Dead Bar, the blue pirate has a sword stuck through him with the handle in the front, later it changes to the back, then to the front again. Seen when the groom falls back and grabs the handle, then picks the pirate up and drops him. (00:19:15 - 00:20:05)
Deliberate mistake: When the crow drops Shelley's ring into Sarah's hand at the end of the film, the sound of metal upon metal is heard. (01:30:00)
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.