Revealing mistake: After King Kong destroys the train track of the oncoming train, in the POV shot directly behind the train operator while he watches Kong rise from the broken track, the small model's support control bar is visible at the right as it moves up and down. The next shot is a close-up of the shocked motorman, and after he attempts to stop the train, there's another shot facing Kong with the control bar visible for a moment. (01:31:50)
Continuity mistake: When the two pigs are running to the brick house, there is no mat in front of the front door, but then when we see the wolf standing outside the house, a mat has appeared in front of the door. (00:05:45 - 00:06:20)