There were two Kong puppets, with differently-shaped heads. The "long-faced" Kong puppet was used for many of the dinosaur fighting scenes and at the top of the Empire State Building. The blunt-headed Kong was used in scenes with Ann Darrow tied to the altar and for many of the New York City climbing scenes. There was also a single full-sized mechanical head built for some of the close-ups. This Kong had extremely white teeth.
The apparent size of Kong changes from 18 feet to 24 feet. This was a conscious decision of director Merian C. Cooper, who felt that Kong's size wasn't impressive enough in New York. The publicity materials would later state Kong's height was 60 feet, almost 3 times the average height as he is actually depicted in the film.
When Kong escapes from his bonds in the theater in New York, he leaves the right cuff of his shackles on his wrist. During the subsequent rampage through the city, the cuff is missing in several scattered shots, and in the entirety of the sequence in which Kong destroys the elevated train. That sequence was reportedly conceived, designed, and filmed when the picture came from the editing room at thirteen reels in length, to which producer-director Merian C. Cooper objected superstitiously. It is easy to see how the cuff would be forgotten in such a situation, but the other disappearances remain a mystery.
(at around 1h 17 mins) The first Skull Island native that Kong bites after he breaks through the wall changes orientation between the long shot of him being picked up and the close-up in Kong's mouth. The head changes direction between shots.
(at around 1h 26 mins) When the car crashes into the front entrance of the hotel it doesn't have any glass in the windshield area. In the next shot, it has a windshield, but with a hole broken into it.
(at around 27 mins) As the crew stand behind the sparse shrubbery to watch the natives performing the ceremony, Ann request to move forward to get a closer look. She does so but when the POV switches to the wide angle shot showing all of the action, Ann is no longer at the front watching the ceremony.
When Kong takes Ann to the edge of the cliff on Skull Island, the animation stand is visible for one frame, accidentally left in the shot for a single frame by the technical artists. NOTE: In the Bluray version of the release, this error has been digitally removed.
(at around 1h 35 mins) As Kong is atop the Empire State Building and just as he is getting shot for the final time, the thin shadow of 'something' is cast across his chest. Naturally if he is up as high as the top of the building there shouldn't be anything that would be able to cast a stable shadow across his chest - unless it is a piece of off-screen equipment that happens to lie between Kong and the lighting.
When Kong is on the Empire State Building, even though it is supposed to be morning, rays of sunlight are poking through the clouds from the west, on the New Jersey side of Manhattan, an impossibility at that time of day.
In the wide shot of Kong climbing the Empire State Building, he is climbing the western face of the structure. The financial district is visible to the south in the background. The shot of him atop the tower shows the Chrysler Building directly behind him. That building being to the ESB's north east, that puts Kong on the southern face of the building. When he falls, in the closer shot, he falls back to the south east. Back in the wide shot, he falls off the western side.
(at around 1h 30 mins) In the sequence where Kong attacks a subway train in NYC, there is no 3rd rail shown, and no sparks as the tracks are torn up. 600 DC volts would have at least given a bad shock to Kong.
Fifteen men chase Kong through the forest. At the end of the pursuit, only Driscoll and Denham are leftover. Nevertheless, when Denham speaks to the audience, he tells them "twelve of our party met horrible deaths". Thus, one man disappears. The explanation: A deleted sequence between the encounters with the brontosaurus in the swampy lake and Kong at the fallen-tree bridge across the ravine. In it, the survivors of the first incident meet three triceratops, and undoubtedly the other "horrible death" occurred here. Armstrong-as-Denham's line, having been shot in early 1932, could not be altered to allow for the cut.
"The natives built the wall on Skull Island to protect themselves from King Kong, yet put a pair of doors on it big enough for him to come through." This is a common misconception. Since Kong can climb the Empire State Building, he probably gets into the compound occasionally; the size of the gate allows the villagers to send him back out.
(at around 1h 24 mins) During the show in New York, Carl Denham refers to Jack Driscoll as "John Driscoll." This is not incorrect, however, as Jack was once commonly used as a diminutive name for men named John.
Kong's fur seems to ripple as he moves, this is due to the indentations made in the fur of the Kong model by the fingers of the men who were constantly touching it to change its position slightly to produce the stop-motion animation effects.
(at around 1h 14 mins) A Skull Island resident jumps from a hut and falls beside a domed chicken cage, which then hinges backwards and catches the actor's wig, taking it off his head, and remaining on top of the cage.
(at around 54 mins) When Kong puts Ann on the tree throne (just before the T-Rex encounter), she moves a meter or so to the left as stop-motion gives way to live-action. Also, because of the full-size tree and actress matted over a portion of the miniature jungle set, part of Kong's paw disappears, seemingly behind the tree but, in fact, behind the matted-in live-action at this moment.
(at around 59 mins) In the middle of Kong's battle with the T-Rex, the tree on which Ann Darrow sits falls to the ground. While this occurs, the stop-motion animation of the two fighting monsters ceases completely and visibly before the end of the wide shot of the falling tree.
(at around 1h 30 mins) As Kong puts Ann down atop the Empire State Building, a matte shot of the live actress replaces the animated model of Ann in Kong's paw, but the matte plainly cuts off a large corner of the shadow thrown by the paw on the building. The same error happens again a few minutes later.
The goof item below may give away important plot points.
(at around 1h 35 mins) When Kong is with Ann on top of the Empire State Building he is shot repeatedly by machine gun fire. He feels his chest with both hands, and touches the blood from his multiple wounds. Yet when he picks up Ann for the last time, no blood is visible on her dress when Kong puts her down.