Revealing mistake: The man from Mars is in an elevator with a woman when the power goes out. He tells her he cut the electricity and gas powered engines all over the world for a half an hour. They proceed to show clips of the power out in different parts of the world. When they get to Big Ben in London, you can see a motorboat cruising down the river in the background. If the boat were powered by wood or coal, there would be plume of smoke trailing it. If it were powered by oil (ie. diesel) electricity is required to pump the fuel into the ejectors. (01:02:05)
Revealing mistake: When Gort goes behind the wall to pick up Patricia Neal, the camera moves about an inch in the same shot, because they had to stop filming, go rig the wires up to Patricia, then start filming once again. (01:17:00)
Revealing mistake: After all of the elecrticity is neutralised, in a street shot you can see neon signs are still working; a huge Coca Cola one, for example. (00:59:30)
Revealing mistake: When Gort begins to walk down the saucer ramp, after Klaatu is shot, the crowd gets scared and runs away. I guess the director found the extras running too slow so he sped up the film. (00:10:30)
Revealing mistake: During the black-out, there's a shot when you see two cars moving in the background. One of them is slowing, which is normal if the engine stops, but the other is parked and then starts moving. (01:01:45)
Revealing mistake: When Gort picks up Patricia Neal, then heads back to the spacecraft, you can see a zipper on the front of Gort's costume, which is never there in any other shots. (01:17:05)
Revealing mistake: When the spaceship arrives in Washington, many people look in the wrong direction. (00:04:20)
Revealing mistake: As Klaatu enters the control room of the spacecraft for the first time, we see the right side panel revolve so he can enter. Once inside, it is the other side of the panel which closes.
Revealing mistake: When the spaceship is going to take-off, every scientists are trying to escape, but there's a man wearing a light colored suit and hat who seems more interested in pushing the chairs everywhere than escaping. He even pushes a chair in another row. The director obviously told the actors to push some chairs to create more excitement in the scene, but he seems to take that too seriously. (01:31:05)
Revealing mistake: In a few scenes the stitches holding together the front and back halves of Gort's "metal" body can be seen.
Revealing mistake: After Gort takes out the guards and Carpenter passes by him, Gort turns around to follow, and the zipper for the costume is visible.
Answer: They said, how they handle their earth problems is no concern to them, it's only if they bring it to outer space and other worlds, they would take drastic measures to ensure that did not happen.