Plot hole: Klaatu is shot and his body is lying in a prison cell. Gort leaves the flying saucer and walks all the way to the heavily guarded police station in downtown Washington DC. Gort is 8 feet tall and is a robot plus he uses his noisy death ray to create a hole in the police station to retrieve Klaatu's body and nobody noticed him? On top of that, he walks all the way back to the saucer unseen with a dead body.
Plot hole: In the scene at Arlington cemetery, Klaatu asks Bobby if it costs money to go to the movies. Bobby states he has $2 his mother gave him, which Klaatu trades for two diamonds. That being said, how in the world did they get from NW DC to Arlington in Virginia, and then on to the Lincoln Memorial at the Mall in DC? Much too far to walk, and Bobby made no mention of money he had before to take a bus or cab.