Revealing mistake: In the library scene when Richie sees Pennywise the clown, all the balloons filled with blood are popping on people who aren't supposed to be able to see them, but one lands on a lady and you can see her jump as the balloon pops.
Revealing mistake: While Bishop and Steve McKenna are practicing with various firearms, a slow-motion shot in the film of Steve shooting a .50 caliber rifle shows that, while the sequence depicts him firing "live" rounds, the extracted shell casing is from a "Blank" cartridge (evidenced by the crimped forward portion of the brass casing). (00:34:15)
Revealing mistake: When the spear handle is protruding from Hector's shoulder, the area of the armor around the circular wound is clearly visible and it is in perfect condition. There is no tear in the armor whatsoever, around the wood, which would have been necessary to allow the wide spear tip to penetrate the armor and actually enter Hector's body as it did. (02:01:20)
Revealing mistake: When Rob is in the Cafeteria eating all the coleslaw, he yells "I'm the coleslaw king of the world!" there is a girl in the background who mouths it as he is saying it. (00:50:00)
Revealing mistake: When the kids step out of the water and walk towards the house, the floor is already soaking wet from previous takes.
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: Near the end of the movie, when Maverick's plane is about to be launched, there is a quick closeup of an F14's nose gear, which is quite obviously not hooked up to a catapult or anything else.
Revealing mistake: In the final Indian chase at the conclusion of the film, when a covered wagon rolls over, one can see the rope that was used to ensure it tipped over.
Revealing mistake: When you see the first shot of the dead Mercutio, he's still breathing.
Revealing mistake: A horse gallops through a field and you can see a telephone pole.
Revealing mistake: It is not what is seen here that is the problem, but what we don't see on the Hogwarts Express; first on the way to Hogwarts when Harry, Ron, and Hermione are in their compartment talking about Draco, and second, during holiday break, when Harry and Ron are talking about Unbreakable Vows. As the camera faces the large compartment window, we see the scenery out the window, but as the train speeds along, the scenic reflection of the windows opposite it, in the corridor, should be seen but isn't. What is reflected is the light colored wall of the compartment beneath the blacked-out window. The camera filming the shots from this angle is positioned at that window, and to hide the camera/crews' outline, the window was covered.
Revealing mistake: The road leading out of the samurai village has distinct tire tracks from vehicles.
Revealing mistake: Candace's eyes are moving and she is breathing after allegedly having been shot and killed.
Revealing mistake: After Wallace kills the Scottish noble in bed, he jumps out of the castle window into a river on a horse. As he is falling, you can see that the horse is a model and when they fall into the water one can see the fake horse bobbing around. (02:15:45)
Revealing mistake: Mrs. Doubtfire sets herself on fire. When she jumps back and starts fighting the flames, it is obviously a stunt double as her face is longer.
Suggested correction: If you look carefully, the face looks pretty much the same, as well as the voice.
The reason the voice was the same is that it was probably an audio dub, which is a voice recording over someone else's voice.
Revealing mistake: When making traps, he's harvesting powder from a spent shell (primer has been struck). (01:05:50)
Revealing mistake: When the final race is under way, the silver Saleen S7 hits a Police SUV and makes it flip, you can see the smoke coming out of the bottom of the SUV where the cannon has fired to flip the SUV.
Revealing mistake: In the scene where Themistocles first talks to Queen Gorgo, in the background you can see several extras, one of which is wearing obvious sneakers. (00:18:35)
Revealing mistake: After Jim's horse is shot from under him while running down the really steep hill, and Jim later regains consciousness, before he turns and finds his horse dead, if you watch closely you can see the horse still breathing.
Revealing mistake: In the first scene at the beach, where Ali carries Stephanie to the water, you can see the shadow of her legs, despite her legs being amputated. (00:41:25)
Suggested correction: Can you? You can see his shadow for sure, but I don't see her shadow cast on anything. I was looking for this mistake on Prime - I added the timecode for the scene too (41:25) in case someone wants to check out and maybe submit a screenshot, too - but I personally can't see it.