Continuity mistake: When the Skull Island natives are holding Ann's arms as the old native taunts her, their grip on Ann's arms and sleeves differ between front and back shots.
Continuity mistake: When Carl and his assistant are driving in the cab discussing who to fill in on the female role, you can see that they pass a tram on their left side. When it cuts the cab is right in front of the tram rather than to its right.
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.
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: When Carl speaks with Hayes and Lumpy about their destination, while aboard the Venture, the towel rags hanging on a line behind Carl change between shots.
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: 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.
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.
Continuity mistake: After Ann and Carl arrive at the docks, as she stands beside the Venture her coat collar is flipped up, then turned down and back up between shots.
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.