While Marilyn is shooting the second scene for her movie, the crew appears to have only one camera. Despite this, the takes of the scene involve her running a great distance, between structures, down stairs, and over a bridge - even though the single camera would have lost sight of her after a few seconds.
When the ape appears at the set of the martial arts movie, the entire crew is seen running away from their equipment to where the actors are standing. A brief shot of the ape is shown, and when it cuts back to the cast and crew, the crew are still standing by their equipment before running back over to the actors again.
In one of the first scenes, two characters driving through Seoul see the Korean World Trade Center, the "North Gate," and the president's mansion. The landmarks are several miles apart, in different parts of Seoul. Considering the short span of time and what appears to be a straight route, the characters wouldn't have time to see all three landmarks.
Not only does the farmer in the village not notice any of the ape's giant footprints until he drives his tractor into one, neither he nor any of the other villagers appear to notice the gigantic ape until afterwards - even though it's standing right in front of them and must have just walked through the village a minute ago.
The giant ape stands and watches the children on the playground for a very long time before any of them notice him, even though they're running all over the place and someone inevitably must have looked in his direction. When he's finally noticed, he hasn't even moved.
The 3D system used to shoot the film had no ability to adjust the level of depth. As such, when viewed in 3D the size of the miniatures becomes extremely obvious since the stereoscopic effect emphasizes their smallness.
Both the shark and snake that the ape "fights" were normal-sized in real life, making them appear inexplicably gigantic next to the supposedly 36-foot ape. Despite this, there is never an acknowledgment by any of the characters that giant animals other than the ape exist.
When the children in the playground notice the giant ape, one of the kids - wearing a knitted cap - first looks straight at the camera when he turns around before shifting his gaze to where the ape is supposed to be.