Revealing mistake: During the scene where the T-1000 is in a truck chasing John Connor on a motorcycle, take a good look at the actual shot of it driving off of the bridge. The street sign is correct, but everything else is backwards! This is because they shot it backwards and flipped the shot during post production. Since the sign was so obvious, it was digitally reversed. However, a good look at the truck's name on the grill will show the shot is backwards.
Continuity mistake: When the Terminator saves John on his bike in the alleyway and the truck explodes in a ball of flames, the Terminator takes his shotgun out and cocks it to aim at an approaching object. After realising it is a flaming tire, he leaves. However, after stopping to relate his mission to John, the Terminator ejects the fully loaded cartridge (which sounds suspiciously hollow when it hits the ground) and reloads again.
Audio problem: John Connors bike is an XR-100, it is a 4 stroke engine. In the movie they dub in the sound of a 2 stroke. It is a quiet little engine so that is why they probably dubbed in the sound.
Factual error: In the final act, when the T1000 falls into the molten steel, he sinks and thrashes around rather like a human in water. However, molten steel has a density of around 8 g/cc - about 10 times that of a human, which means T-1000 must weigh about 1600 lb / 700 kg, and is therefore too heavy to do many things we've seen: ride a Kawasaki KZ1000P (up a flight of stairs) without collapsing the frame and blowing out the tires; be dragged by hooks in the lid of a car trunk without peeling the lid like a can opener or ripping off the trunk lid; jump onto the back of a car without collapsing its suspension; operate a helicopter in level flight from either pilot's seat. If he's light enough to do those things he'd basically sit on the surface of the molten steel and fry. Either way there's a mistake somewhere...
Factual error: There is absolutely no way the Police would send a helicopter to a crime scene with only the pilot on board. He has to fly the helicopter close to buildings, trees, power lines, and he may come under fire or have to manoeuvre out of any one of a number of crisis situations, and fast. He cannot possibly serve as an observer or pass on situation reports as well as controlling his aircraft. The fact that they needed an empty seat for the T-1000 is no excuse; he would have an observer on board with him.
Continuity mistake: In the Steel Mill scene, Sara has 8 shells. She shoots the T-1000 once (7 left), then she drops an unused shell (6 left), then reloads (5 left in theory, but there are now 6 on top of the gun). Later she loads the shotgun with the other 5 shells (one's disappeared, but it's back to what there should be) and recocks the gun, ejecting the other good shell. Later, she nearly kills the T-1000 by shooting him with 7 shells.
Continuity mistake: When the T-1000 is entering Dyson's house, he hears on the police radio that Sarah Connor is at "2144 Kramer." Later, just as the police show up at Cyberdyne's offices, the voice over the radio gives the address as "2111 Kramer."
Revealing mistake: When the Terminator is in the elevator and the T-1000 forces the door open, the Terminator shoots the T-1000 in the head. If you look closely you can see that the T-1000's head is already split down the middle.
Revealing mistake: After the T-1000 steals the truck and throws the driver out there is a big action sequence where the truck hits a lot of cars. In one scene the truck hits 2 cars which were both already stopped across the road front bumper to front bumper, blocking the road in the process, making it impossible for the truck to miss them.
Continuity mistake: The tanker truck is shown having two headlight lenses on each side on the front. During most of the chase the inside lamp is lit, but when Arnold shoots it with the grenade launcher the outside lens is lit. The next shot shows the inside lens lit again, but then when Arnold climbs on the hood of the tanker to fire through the windshield the outside lamp is again lit.
Visible crew/equipment: [Special Edition only] Shortly after the Terminator shoots up the police cars outside Cyberdyne, the SWAT team enters the building through the front glass doors. When the shot changes from outside the building to inside, the camera dolly and cameraman are visible in the reflection on the glass doors and windows.
Revealing mistake: When the T-1000 is chasing John in the transport truck cab, the sparks always appear before the truck actually hits the walls.
Revealing mistake: After the T-1000 finishes battering the Terminator with the beam, the Terminator drops to the floor and starts dragging himself. When you see the stump of his left arm move forward then backwards, the string moving the stump is visible.
Revealing mistake: In the beginning of the film, when the biker is thrown onto the stove you can clearly see the valves where the steam is coming from - it's NOT from his hands.
Factual error: The truck that the T-1000 uses to try and run down John in the overspill, is a Freightliner FLA 9664, which uses a diesel engine - it does not use petrol. Diesel is much harder to combust in comparison to petrol/gasoline, and the spark from the battery cables on the spilt diesel would absolutely NOT ignite under those circumstances.
Continuity mistake: In the scene where the Terminator has grabbed John and won't let him go until he tells him to, the Terminator almost shoots two guys who come to help. John tells him to put the gun down, which he does. Now, when John picks up the gun to hand it back to the Terminator, it goes from being cocked (the hammer pulled back) when it is in John's hand, to uncocked when Arnie takes it, to cocked again when he puts it in his belt.
Continuity mistake: When John Connor holds the Terminator's jacket up to the light in the shed in Mexico it's full of holes. You see the back of it when they leave (to chase Sarah) and there are no holes.