Continuity mistake: In the opening scene, a Norwegian helicopter is flying across the Arctic. The co-pilot is half outside it. From the exterior angle, the co-pilot has a pair of binoculars and is looking directly downwards with the binoculars also positioned directly downwards. In the next shot, from a side angle, the binoculars are suddenly elevated and he is looking directly forward. (00:02:55)
Continuity mistake: When the Norwegian helicopter finds the dog running in the snow, the dog turns around to notice the helicopter, causing some of the snow around him to push upwards a few inches. The shot cuts to the helicopter, but when the shot cuts back, the snow is suddenly almost level with the rest. (00:03:35)
Continuity mistake: After the scene where the Norwegian helicopter chasing the dog through the snow ends, the scene cuts to the research station. The first shot from the research station shows a sign: UNITED STATES NATIONAL SCIENCE INSTITUTE STATION 4. This close-up shows scratching and rotting all over. A few minutes later, as the helicopter arrives at the station, the scratching and rotting over the "4" is no longer there. (00:04:30 - 00:06:15)
Other mistake: The brief chess game (four moves) shown in the beginning of the movie makes absolutely no sense. For instance: There are no white bishops on the board, but after the human player taps a few buttons, the computer says that he just moved one. Within the two moves described first, the positions of the pieces change completely. In addition, some pieces are now gone and there are new pieces on the board. It's like an entirely different game. The final move is said to have been made with a black rook, which is impossible. In the shot shown before this move, there is not a single position available to that chess piece that would result in an instant checkmate. Nothing in the editing indicates that these few short shots are supposed to be viewed as separate games. (00:04:50)
Continuity mistake: After the Norwiegans' helicopter has chased the dog-Thing to the American research station, the chopper flies around the station before landing on the ground. Before landing, MacReady is shown exiting the watch tower with a bottle of alcohol in hand. When he exits, the bottle is around his hip area. Then from an angle of MacReady low down, the bottle is suddenly raised slightly up to his chest area. (00:06:35)
Continuity mistake: When the helicopter is circling the research station, the co-pilot picks up a hand grenade to throw on the ground. He picks up the grenade on the bottom row in the middle column. There is no grenade in the middle column from the second row of grenades and no grenade in the left hand column of the top row of grenades. Around 45 seconds later, in the shot after the dog leaps onto one of the researchers, the exact same shot of the man taking the grenade out of the box has been repeated a second time. He takes out the exact same grenade from the exact same row. (00:07:15 - 00:08:05)
Continuity mistake: After the Norwegians exit the helicopter, one of them goes to throw a grenade but accidentally lets go of it, and it explodes. In the shot where the man takes cover during the explosion, the fire clears out and there is soot around the helicopter on the snow, about six feet. A couple of shots later, as the Norwegian stands up, the amount of soot around on the snow has notably increased. (00:08:20)
Deliberate mistake: When the Norwegian starts shooting at the dog, Childs jumps into the snow and you can see the shape before he jumps in where he's had to do this before on different takes. (00:08:40)
Continuity mistake: Just a couple of minutes into the movie, Gary shoots dead the crazed Norwegian and the camera returns to MacReady. Now watch closely: When he gets up to help injured Bennings, he and his Jim Beam bottle are covered up to the hilt with loads of snow. But on the next shot, a split second later, his clothes are miraculously clean and the whiskey bottle as dry as you can possibly get it. (00:09:00)
Visible crew/equipment: When Windows is in the radio room, he is trying to communicate with McMurdo. Doctor Blair then enters the radio room and approaches him, tapping his shoulder. Windows then pulls his headphones down from his ears and has them placed around his neck and he then says to Doctor Blair, "Nobody." Just as he says this, there are two white screens visible in his glasses. (00:11:00)
Visible crew/equipment: When Nauls is in the kitchen cooking and the camera moves towards the room next door, the shadow of the camera is visible on the right wall. (00:14:35)
Visible crew/equipment: Just after Nauls is told by Bennings to turn down the music the film cuts to a tracking shot going towards the rec hall. At the very beginning of this tracking shot keep an eye on the lower half of the medical cabinet, and you can easily see the dolly that the camera is being pushed on. If you look just above the dolly you can make out the blue sweater sleeve of the crewmember pushing the camera as well. (00:14:55)
Visible crew/equipment: Bennings tells Nauls to turn down the Superstitious song and Nauls skates over to the radio, but then doesn't turn the radio down at all. The shot then cuts to a shot of the medicine room which then continues as a panning shot and pans into the next room. Just as the camera stops panning and the shot remains still, there are a few stage lights visible reflected in one of the cabinets on the right hand side of shot. Those certainly aren't lights because all of the lights in the room are switched off. (00:15:10)
Continuity mistake: When MacReady and Doc are examining the abandoned shack, MacReady comes across a portable video unit and MacReady then wipes off the snow and dust off the unit. From the first shot of the unit, we can see part of the unit is wiped so far, we are able to notice the unit itself. The visible part of the unit is located in the middle of the unit at first, but after Doc states the papers are in Norwegian and the shot cuts back to MacReady, it is now the edge of the unit that has the top of the unit visible. (00:20:00)
Continuity mistake: MacReady and Doc return to the research station from the abandoned shack in the helicopter. The scene then cuts to the dog watching the two exit the helicopter in the window. In the shot where the helicopter is visible in the window, the dog is looking out of the window from the right hand side. In the next shot, it is suddenly looking out of the left hand side. This mistake has nothing to do with the angle of the camera. (00:22:35)
Continuity mistake: When the stray dog is placed in the cage with the other dogs and starts to mutate into The Thing, one of the other dogs start biting a hole in the fence. We get a clear view of the hole in one close-up, and in the next shot as The Thing sprays liquid on the dog, and the hole in the fence is much bigger. (00:27:45)
Continuity mistake: Just after MacReady overhears the dogs barking, he runs over to the fire alarm, breaks the glass with his beer can and pulls the fire alarm. After he breaks the glass, there is a piece of broken glass located next to the alarm. But in the next shot, as he removes his hand, the piece of glass has vanished. (00:30:10)
Continuity mistake: When the dog, aka the The Thing, is led into the dog pen for the first time we see the floor is covered in a thick layer of straw for the dogs to sleep on. This is seen every time except when Childs uses the flame thrower. We get a wide shot of the pen as it's lit up in flame and the floor is now completely bare of any straw. There are also none of the recently deceased dogs that were lining the floor, being converted into Things. (00:31:05)
Continuity mistake: When MacReady and the two other researches first discover the the spacecraft, there is a shot where the camera is in front of the three looking downwards into the hole. All three of them have their hands by their sides. In the next shot, the researcher on the left suddenly has his arms raised with binoculars suddenly in his hands. (00:38:20)
Continuity mistake: After MacReady and Doc have discovered the spacecraft, the scene cuts to a wide angle of them approaching one of the researchers looking into a dug up hole. Just as the wide shot ends, MacReady and Doc are standing right next to the man. The shot then cuts to a closer angle of the three and MacReady and Doc are now several feet away from him. (00:39:50)
Answer: The death of Fuchs is probably the best answer to this question, as it appeared that Fuchs burned himself alive before the Thing could assimilate him. It's also possible that Norris suspected he was infected before he transformed. There is a scene in which we see Norris, who is alone, suddenly wince in pain, surprised, and grab at his chest, but he continues functioning normally thereafter. Following the altercation with Mac, Norris collapses and becomes unresponsive, until his chest cracks wide open and bites off Copper's arms. Also, in the blood test scene, Palmer's facial expressions appear to betray his secret, but he was already fully transformed at that point.
Charles Austin Miller