Revealing mistake: In the scene where the Terminator and the T-1000 are fighting in the corridors of The Galleria, the Terminator has fired multiple shots at the T-1000. When he gets up off the floor, the Terminator throws him into the left wall and the impact hole is already visible before he hits.
Revealing mistake: When John Connor and the Terminator are at the payphone calling his step mom, the Terminator punches the phone and puts a massive dent in it and change comes out. If you look at the bottom of the phone before he punches it there is already a dent there. [Pan & Scan version ideally, although you can just see the very top of the dent for a few frames in widescreen]. [ALSO- you can see that the area where Arnie hits the phone is merely plastic, which is unpainted to match the black phone!]
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.
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.
Revealing mistake: When Arnold begins to beat up and throw around the workers of the hospital, the African American worker is thrown into a window. If you look carefully you can see that the window he is thrown into is a different kind of glass than the other windows that surround it, indicating that this is not real glass. You can also see that none of the other window frames of glass on the inside of the corridor. There is just the metal frames covering the windows. In some shots later in the scene when the T-1000 is chasing them down the corridor you can see the bits of glass that were left over from before have disappeared.
Revealing mistake: When the T-800 is being attacked by the SWAT team in the Cyberdyne building, notice that in most of the shots (i.e. when he is being shot in the face, and also when the camera is behind him) Arnie has been replaced by a dummy. When the T-800 pulls out his gun and starts shooting the SWAT team, it's now back to the real Arnie, and notice how none of their bullets are now hitting his face and body, even though shots are still being fired.
Revealing mistake: In the scene where John is helping Arnie up after the T-1000 has been exploded and sent to his doom in the fiery pit of molten steel (Arnie is saying "I need a vacation"), you can see how the effects crew haphazardly put on a fake busted mechanical arm underneath Arnie's coat and how it bulges out from his shoulder. You can almost see how they just tied Arnie's arm back behind his back and put a fake arm over him.
Revealing mistake: When the T-800 and T-1000 first begin to fight in the steel mill, the T-800 puts his fist through the T-1000's head causing him to revert to liquid metal form, then as the T-1000 is throwing the T-800 from side to side you can obviously tell that the T-1000 is just an actor wearing a highly metallic mylar suit in some shots.
Revealing mistake: Early on in the film, the T-800 sees John riding down the aqueduct. He stops, and a blue car skids and is hit by another on its right side near the rear wheel. As the T-800 sets off in pursuit of the T-1000 and John, a blue car skids and is hit on its left side. Guess what? Its the same car as earlier. You can tell by the massive dent above the rear wheel.
Revealing mistake: In the scene where Sarah opens the skin and endo skull of the Terminator, you have a shot where you see the reflection of the Terminator, Sarah and John in the mirror. When the camera takes a shot from the back of the Terminator, you see the back of a puppet on which the real Sarah is performing the operation. In the reflection you see no camera, the real Terminator, and doubles of Sarah and John. Especially the moment Sarah puts down the screw driver, the reflecting screw driver is put down a fraction later than Sarah's.
Revealing mistake: Special Edition. The biggest giveaway about the false mirror in the 'chip removal' scene is that John's 'reflection' has his back to the mirror when Sarah is drilling, whereas the real John is standing side-on to it. Also notice that John nervously looks at the camera in this shot.
Revealing mistake: In the scene when the T-800 first comes through the time machine, in the shot where he stands up. If you look towards the right side of the bowl shape that's melted into the ground, you can see that the bowl shape is actually above ground. There's a shadow being cast by it on the right side.
Revealing mistake: In the scene where the Terminator has just broken Sarah out of the hospital and the T-1000 has been shot off the back of the cop car you can see his "metal" arms bending as he rolls across the pavement, and as he gets back to his feet you can see where his real hands are.
Revealing mistake: When the cop by the vending machine is about to be killed by the T-1000, the back shot of him reveals he's been replaced by an obvious doll: His perfectly trimmed hair along the nape is now long and messy, and a long stitch appears along his sideburn and down to the neck.
Revealing mistake: After the Terminator has jumped on to the truck and shot the T-1000 full of bullets he pulls the wheel to the right so that the tanker truck skids and falls but if you look closely you can see that the stunt double for the T-101 merely fakes he's pulling the wheel, and then holds onto the cab and you can see the stuntman for the T-1000 inside the cab turning the wheel before it flicks to the wider shot.