Best action movie mistakes of 1984
Audio problem: When the Terminator breaks into the police station, he has an auto-shotgun in his left hand, and a machine gun in his right. Before he kills the power in the building, he comes to the end of a hall, points his shotgun through a doorway, and shoots. A machine gun sound is used for the blast, instead of a shotgun sound.
Other mistake: Indy's bridge breaks and he is hanging by it with the natives shooting arrows at him. If you look closely you can see two arrows bounce off his back. All the other clatter noisily onto the cliff-face or stick in the bridge, so it's not like they've lost much force due to the range.
Revealing mistake: Conan and his party flee from the temple guards and escape into the crypt, closing the huge stone door behind them. A moment later, the camera shows the leader (Ferdinand Mayne) standing at the foot of the steps holding a torch. He chucks the torch out of sight to his right and begins walking towards the door. If you look closely you'll see the torch disappear nicely out of sight behind the wall as if he had "passed" it to someone standing there.
Factual error: According to "The Doomsday Machine", full impulse drive is one-quarter the speed of light. In the first two movies, Enterprise used thrusters as opposed to impulse drive to leave Spacedock, confirming the notion that impulse drive is far too fast to leave such a (comparatively) small structure. Styles, however, orders Excelsior to one-quarter impulse, which is 18,750 km/s. In one second, she will travel half again Earth's diameter. From the time he gives the order to the time we see Excelsior clear spacedock's doors is approximately 40 seconds. Even allowing 30 seconds to go from rest to one quarter impulse, spacedock must be 13-15 times bigger than Earth! That's some serious engineering.
Revealing mistake: When Supergirl flies through the window to fight the invisible monster, half of the screen shows her jumping in a school uniform and the other half exiting with the Supergirl outfit. Watch closely and you'll notice that her halves don't match, giving the sense that she is missing part of her body.