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.
Continuity mistake: When Ann is about to steal the apple, she picks up a different apple first. When she is about to put it back, the angle of the apple in her hand changes. Watch the apple stalk and you can see it.
Audio problem: When the ladder Ann was standing on hits the ridgy part of the Empire State Building there is no loud crash.
Continuity mistake: After the screening of Carl's movie he walks down and says "The script has been re-written", while he has his left hand up by his waist. When it cuts his left hand is hanging down.
Continuity mistake: During the whole film, even though Ann is thrown about and man-handled by Kong, as well as sliding down rock and cliffs in bare feet, and falling over numerous times to escape the many creatures and dinosaurs, she ends up with virtually no marks or scratches on her body. Her dress is dirty, but that is about it. Her hair also stays reasonably in place. Surely she would have been scratched and bruised all over her legs and arms from the trauma.
Continuity mistake: In the scene where the boat is leaving NYC and the camera is panning around it - the smoke from the ship "follows" the camera by always pointing to the right relative to the camera view; even though it should be trailing backwards, opposite of the ship's direction.
Continuity mistake: When Kong has grabbed Hayes, he tells the rest of them to get out of there. As he says "Do as I say", his gun is pointing at Kong. When it cuts he suddenly has his other hand on the gun cocking it.
Revealing mistake: As Kong and Anne Darrow exhale in the freezing New York air there are many shots where you can't see their breath frosting up as it comes out of their mouths.
Continuity mistake: In the scene where the movie star is trying to talk them into giving up he has a rope slung around his chest over one shoulder. He never takes it off, but when he leaves he no longer has it, and Adrian Brody is holding it.
Continuity mistake: When the old man says he is moving back to Chicago, Ann hugs him and place her hand around him right below his neck. When it cuts her hand is lower down on his back.
Continuity mistake: While telling Carl about the shipwreck sailor the crew of the venture picked up on an earlier cruise, Lumpy keeps whittling on a piece of scrimshaw. He continues to do so when Carl is about to leave the galley. In the next shot, when Carl turns back to give a reply, Lumpy's arms are suddenly lowered at his side.
Continuity mistake: When the main characters first arrive on the island and are attacked by the natives, one of the natives attempts to decapitate Carl but Englehorn arrives at the last minute and saves him by shooting the native three times. As he is falling, it is very noticeable that there is not a scratch on him. He never bleeds at all, there is not even an entrance hole for any of the bullets.
Factual error: In the scene in which Kong is running loose on the streets of New York city, and being chased by two military Army vehicles, the vehicle identification number, starting "USA and followed by six or seven numbers" is visible on the hood of the vehicles. The first two numbers in a USA number is the year of manufacture of the vehicle. Thus, the truck with the 3 inch cannon was manufactured in 1945 because the number starts "USA45." The time setting of the movie is 1933-1934.
Revealing mistake: When Kong is shaking the tree down it's obvious that there's a screen behind the film crew when they fall.
Continuity mistake: When Ann is caught stealing the apple, Carl pulls up a coin saying "Excuse me. Ma'am, I think you dropped this". The way he holds the coin differs in the next shot.
Factual error: There is no lift in the Empire State Building running between 1st and 100th, as shown on the dial in the lift.
Visible crew/equipment: As one of the Venture crew members picks up a chloroform bottle from a case, you can see a bright studio spotlight reflected in the bottle.
Continuity mistake: When the sound engineer says "We're gonna have the ship's engines all over the dialogues", he has his left hand to his headphones. When it cuts his hand is gone, but in the next shot his hand is back on the headphones.
Continuity mistake: Jack and Carl are in Carl's stateroom. Carl opens the crate of whiskey, takes out a bottle and puts it down. The bottle then turns itself around so the label's sometimes visible, sometimes not.
Answer: They scared them off with their guns. In the scene where they capture Ann to sacrifice her to Kong, Denham and his men come to rescue her and when they start shooting the natives hide. It's never fully explained but the most likely answer is that they are too scared and have even moved villages or are just hiding really well.