Continuity mistake: When Carl is convincing Ann inside the diner, after she stands up and Carl convinces her to accept the role, there's a waitress behind Carl about to walk towards her. A split second later, while Carl says "she's the saddest girl he's ever met", the waitress appears 12 feet away, and is now behind Ann way at the end of the diner.
Continuity mistake: Ann is soaking wet when she is being led through the natives. When she gets to the top of the wall she's dry.
Continuity mistake: When Carl falls at the beginning of the brontosaurs chase we see that he is only just in front of the brontosaurs so when he fell he should have been crushed straight away but he isn't. Jack then runs to help him and we see that the brontosaurs only need another step or 2 (which would take 1 or 2 seconds) before they reach Carl and Jack. Carl gets up and argues with Jack for 5 seconds or so by which time they should have been crushed. They then run and there is a far off shot showing the brontosaurs back where they were at the start again.
Audio problem: When Carl tells Preston to show Ann on board the ship he says something like, "Hello, Miss Darrow, I'm Mr. Denham's assistant." His lips aren't properly synchronized with the dialogue when he says this.
Continuity mistake: Kong continues to change size during the movie. The most obvious way to notice this is when his hands are near Ann. When Kong first finds Ann in NY, his hands are 3/4 the size they are immediately after when he picks her up.
Continuity mistake: When it cuts to the filming of the first take between Ann and Bruce on the ship, it shows Jack standing on the right side of the picture, about a feet away from the wall of the ship. When it cuts to a close-up of Jack, he is suddenly leaning against the wall.
Revealing mistake: Despite being thrown, falling, being dragged and various other things, Ann's hair and face are almost always clean. Even when there does appear to be some dirt, in the next shot they are clean again.
Continuity mistake: When Kong is about to fight the last Rex, Ann begins to back under his arms. In a distance shot we see that she is already a fair distance behind his arms, underneath him. Cut to Kong noticing this, then cut back to a back shot of Ann backing under and she has not even reached his arms yet.
Continuity mistake: Before going on board the ship, Captain Englehorn asks Ann if she is nervous while he lights his cigarette. You can see his cigarette remains in his mouth, but when it cuts it's no longer in his mouth.
Continuity mistake: Aboard the Venture, when Ann runs into Jack with her "good legs" she has a towel on her shoulder, which changes position until she goes to her cabin.
Continuity mistake: When Kong is at the top of the Empire State building we see Ann start to climb the ladder and she is only a few rungs up when the camera view changes. When it cuts back to her, she is still climbing those first few rungs.
Revealing mistake: The crew is sailing to the island and the rough sea makes the boat move violently. Jack Driscoll stumbles but the things in his cabin don't move at all, or at least don't cause the chaos they should. Obviously the only thing moving is Jack and the camera.
Continuity mistake: In a scene at the very top of the Empire State Building, Ann hugs Kong's left arm. In the very next shot, she is standing right in front of Kong, between both of his arms.
Continuity mistake: When Ann and Jack are about to kiss the first time, there is a close-up of Ann's face. When it cuts Jack's hand suddenly appears on her face.
Continuity mistake: When Ann is dancing in New York while King Kong is enchained, her hair is straight and then curly in the ends. But when she goes out in the streets and sees the Kong poster her hair is wavy. When she finally meets Kong again her hair is back to straight and curly.
Factual error: In the scene where Kong is running around New York City and is being chased by the Army, the first military open-topped sedan (which has a machine gun mounted in the rear seat) has a 1934 NY license plate on the front of the car. Military vehicles do not have civilian license plates, not even as a decoration.
Revealing mistake: When the longnecks are tumbling down the hill it's obvious there's a screen behind Preston and Jimmy and Hayes.
Revealing mistake: When Ann is in Kong's hand for the first time you can see a screen bounce behind Ann.
Continuity mistake: When Carl steps out of the room after screening his movie he doesn't cast any shadow on the door behind him. When it cuts his shadow suddenly appear on the door.
Continuity mistake: In the scene where Jack Black and Adrian Brody are talking on the boat (as it's getting ready to leave), when the camera is focused on Jack, the cityscape behind him (through the window) is moving (as if the boat has started moving), but when it focuses on Adrian, the cityscape behind him (through the window) is not moving.
Chosen answer: The original creator of King Kong, Merin C. Cooper, wrote a novel adaption of the movie in which it was explained that the gates were built by a earlier culture of islanders that were friends with the "Kong" race. The "Kongs" helped the original islanders to build their village and the wall (thus meaning the gate had to be big enough for the giant gorillas to walk through). By the time of the events of the movie, the original islanders have "died out" and their old village had been taken over by a race of more primitive natives who became enemies with the Kongs, and were trying to use the gates for safety.