Revealing mistake: When the T-Rex has a raptor in its mouth at the end, the raptor disappears completely from the T-Rex's mouth for one frame. It's just after it's picked up - the T-Rex swings it left, then right, and as it swings to its left again the raptor disappears. If you want to be even more precise, there's a slatted/stepped white bit above the door - the raptor disappears about 3 frames after its foot moves above that white bit.
Revealing mistake: After the T. Rex has flipped the Explorer upside down there's a closeup of Ian, and when it cuts to the T. Rex chomping away on the tire while the Explorer moves around, we can see that the acrylic glass roof is attached to the vehicle with thin cable wire - holes were drilled in the acrylic glass roof and sides of the vehicle.
Revealing mistake: While the T. Rex attacks the Explorer that Lex and Tim are in, during the stunt as the acrylic glass roof comes down on the kids in the interior shots, the strip of duct tape falls through the opening and dangles from the roof of the vehicle - presumably the tape was holding the acrylic glass roof in place before the stunt.
Revealing mistake: While the T. Rex attacks Explorer 4, when Lex and Tim are holding the roof up with their hands and feet, in one of the interior closeups after the T. Rex has lost its tooth we can see the metal post jutting out from the dinosaur's gum, to which the fake tooth is attached in the animatronic's mouth.
Revealing mistake: When Nedry is attacked by the Dilophosaurus, (the spitting dinosaur), the first spit supposedly lands on his shirt, BUT if you look closely, Nedry slaps it there himself with his hand - there's only a little bit on his shirt before he hits himself, then there's loads.
Revealing mistake: During the scene where Dr. Grant and the children are forced to climb a fence to flee from an unseen dino, there's a brief side view of the fence that clearly shows that it isn't continuous - it is probably only about 75 feet wide.
Revealing mistake: When the T-rex is attacking the vehicle and he has turned it over, the camera pans round behind the T-rex and you see through its legs, the ground all around the base of the beast is dry, but it's been pouring with rain for a while.
Revealing mistake: When Grant is trying to save the two grandchildren in the over-turned Explorer, the T-Rex returns and surprises them. Grant holds the girl and tells her not to move. The Rex then starts smelling around and blows Grant's hat off. Well if you watch closely, you can see that the air that blows Grant's hat off doesn't come from the T-Rex, it comes from something under the Rex.
Revealing mistake: When Lex and Tim are playing hide and seek with the Raptors in the kitchen, when the camera cuts to a wide shot of the Raptors walking in from a distance, the Raptor on the left looks directly at Tim while he crawls by, but then looks back in the direction it was going.
Revealing mistake: When the Dilophosaurus spits at Nedry, you can see the smoke from the gun used to shoot the spit in his face, top left of screen.
Revealing mistake: When Grant tells Lex and Tim about the breeding he then gestures to the dinosaurs' footprints. Some of the footprints are very square in shape and have obviously been stamped in the ground.
Revealing mistake: When Ellie runs from the Raptor the stunt double who runs for her has on a wig that looks nothing like her real hair. It just looks very fake.
Revealing mistake: When Alan and Lex are holding on to the cable, fearful of the Explorer that is about to come tumbling down at them, you'll notice that the car, if it had been filmed at the same time the actors where there, would have cut off Sam Neill's leg. Lex grabbed the wire in time but Sam doesn't move his leg enough.
Revealing mistake: In the sequence when Lex almost falls from the hole in the ceiling, she looks straight back up at the camera. Rather than cut away from the stunt double at this point, they actually bothered to CGI the actress' face over the top so they could use the sequence right through. Unfortunately you can tell what's been done.