Continuity mistake: When the T-rex is attacking the vehicle with the kids inside, Alan gets out of the other car. Even though it is pouring rain and Alan is standing perfectly still, no raindrops are seen hitting his solid, medium-colored shirt. It stays perfectly dry, even though there is nothing overhead that is shielding him from the rain. It is only after the scene cuts to him at the other car that the shirt is suddenly drenched. The rain is obviously CGI.
Continuity mistake: In the scene when Ellie is in the bunker trying to escape from the raptor, she stumbles along the floor gratings and is dragging her flashlight connected to an ankle bracelet. It appears securely connected as indicated by wildly bouncing and being flung around. She bashes her way through the door and slams it behind her, then she runs, suddenly free of the flashlight and connecting strap. If it was as securely attached as shown, she should have had a devastating fall when it was caught in the door, and the raptor would have won.
Factual error: At the beginning of the film we are shown an amber mine in the Dominican Republic. This amber is only 45 million years old, Hammond would never bother buying the amber from there as dinosaurs disappeared from the fossil record 65 million years ago.
Continuity mistake: When Grant shoots at the window in the control room, and we see the holes, they are holes from rifle bullets. But the shell casings on the floor is from a shotgun. And yes - shotgun shells do exist with one big slug in them, but then the holes in the glass would be a lot bigger.
Continuity mistake: After Nedry has sprayed the shaving cream on his hands, (and after placing it on the pie) we see a sideview shot where he lowers his hands to his sides. The shot changes to the front and his hands are up again, drying his hands off with a napkin. It was too fast to move his hands.
Continuity mistake: When the five characters start to leave the helicopter upon arrival on the island, Richard Attenborough is not sitting opposite Jeff Goldblum as he was moments earlier as the helicopter descended to the pad.
Continuity mistake: When Grant nearly passes out after first seeing the Brachiosaurus, he sits down on the grass. In the following shot, he is shown kneeling.
Continuity mistake: In the scene from behind Dr. Grant we can see the cow being lifted straight up. You can see that the cow is rather close to Dr. Grant. Then the scene cuts and the cow is already in the middle of the top of the Velociraptor paddock. Judging from the distance between Dr. Grant and the paddock from the previous wide-shot, and the fact that Dr. Grant made no big moves, the crane couldn't pass that distance between the two shots. (00:27:35)
Other mistake: When Alan, Lex and Tim are climbing over the perimeter fence and the buzzer begins to sound, Alan and Lex have come off the fence on the other side and Tim loses his footing further up on the fence. He begins to pull himself up, but in the very next shot, a person is seen coming down the fence closer to the ground in khaki shorts and boots. Tim hasn't moved from his position further up, so it can't be him, and Alan and Lex were already on the ground, and did not have khaki shorts on. (00:43:15)
Continuity mistake: In the scene with Dr. Grant and Lex standing nose-to-nose with the T-Rex, the dinosaur sniffs at the humans, then turns its attention to pushing the Explorer around as Grant and Lex scramble for safety. When the T-Rex starts pushing the Explorer, a profile shot shows that the monster's foot is no more than two yards from the vehicle; yet, in the immediate next shot from the monster's point of view, the T-Rex is obviously positioned 10 or 15 yards away from the Explorer, much too far away to be pushing the vehicle.