(at around 5 mins) The chess moves spoken by the computer don't match the ones on the screen; also screens are shown from different games.
All exterior shots of the tool shed where Blair is imprisoned show the window next to the door has been boarded up with the boards horizontal. However, all interior shots of the shed show that same window with the boards attached vertically.
(at around 1h 12 mins) Childs breaks down the door with an ax, doing extensive damage to it, but several scenes later, the door is intact except for one ax hole.
(at around 7 mins) Norwegian pulls the same grenade out of the box twice.
(at around 1h 13 mins) As Mac comes out of the supply room with the flare and dynamite, the TNT sticks he is holding are almost falling apart and he is holding them by one stick. In the following shots of Mac the TNT sticks are suddenly wrapped tightly with black tape again and he holds all the sticks.
Flamethrowers would be useless in Antarctica, especially outside. Gasoline (even in the form of napalm) has too high a freezing temperature to be forced out of a tank without solidifying. While there may be heating torches used, these would probably be LNG (liquified natural gas) and not napalm. They also wouldn't shoot flames out as far as a flamethrower.
(at around 44 mins) MacReady says "It's forty below outside." That would be a freakishly warm winter day in inland Antarctica, where winter temperatures are closer to minus 80 Fahrenheit (minus 62 Celsius).
During the many interior scenes where the flamethrowers was used, resulting in large fires being started and then extinguished by the characters, the rooms the fires were in would be left with thick choking & blinding smoke, yet you see the rooms are always smoke free after the fires are put out.
This story takes place on the first day of winter. This is on the winter solstice which for Antarctica is in June. At this time of the year, Antarctica should have no daylight hours yet the first half of the film is bright day.
Characters wearing glasses go from the severe cold outside, to the apparently toasty warmth inside the buildings, without their glasses fogging over.
Between the time Fuchs talks to Mac about Blair's notes, calling the snowcat 'the Thiokol' (another brand of snowcat) the logo and model changes from a Skidozer 301, with its model name between the headlights, to a 302, with the Bombardier lettering between the headlights and the model name lower down to the left side (screen right). When they take Blair out to be locked up, the snowcat is again a 301 (you can see the blue model-plate between the headlights, not the black-on-yellow of the 302's Bombardier lettering). This is no goof. It is shown multiple times, that they're using more than one snowcat. In some wide shots of the camp the vehicles are visible.
"Regardless of whether he had expert "alien" knowledge, it is ridiculous to assume Blair had time to dig an underground tunnel and half build a spaceship in the few hours he was locked in the shack." It is important to note that Blair spends several days locked in the shed, and it is implied the basement already existed and was not constructed by Blair. The Thing can also take any shape and it's entirely possible Blair-Thing took a form that allowed it to quickly assemble the ship, such as using several tentacles or limbs that could build different parts of the ship at once.
(at around 1h 23 mins) When one of the characters is slammed into the ceiling, a piece of the ceiling breaks off, but instead of falling to the ground, it "falls" upwards into the ceiling, revealing the scene was shot upside-down.
(at around 8 mins) When the Norwegian is firing on the American scientists at the beginning of the movie, we clearly see that Childs has already jumped into the snow in previous takes of the scene. We can see a shape on the snow.
The infected Palmer attacks Windows, throwing his bloody corpse against a ceiling lamp and then onto a shelf. As Windows hits the wooden shelf, the top piece clearly bounces like its rubber.
(at around 18 mins) While they are looking at the ice block in the Norwegian base, several of the icicles can be seen swinging.
(at around 25 mins) When Blair does the autopsy on the burned creature he takes out the inner organs like they were lying loosely in the body.
(at around 1h 23 mins) After Palmer's blood leaps from the dish after being scorched by Mac's flamethrower, we see Palmer (David Clennon) morphing into a Thing-monster. Several men tied to a couch are now screaming in terror for their lives. We hear Nauls's (T.K. Carter) screaming loudly but when the camera catches some shots of Nauls, he's just sitting their placidly when the soundtrack simultaneously reveals him to be screaming.
(at around 4 mins) While the guy in the chopper with the rifle fires several shots at the dog, and we hear the sound of a gunshot on the soundtrack, at no time do we ever see a muzzle flash from the end of the rifle.
(at around 15 mins) As the camera pans through the empty camp, after Bennings calls Nauls on the intercom, it casts a shadow next to the blood storage.
(at around 15 mins) Right after Bennings yells on the intercom to turn the music down and we see his request ignored by Nauls in the kitchen, the following scene that slowly dollies from right to left in the empty medical room, the moving wheels of the dolly and a man in a light blue shirt pushing the dolly are clearly seen in the reflection of bottom and top pane of glass of the stainless steel and glass medical cabinet. Especially visible on the Blu-ray version.
(at around 1h 30 mins) As the men come down the stairs into the generator room, Nauls and Garry head down a second flight of stairs as Mac holds up a flare. The shadow of a crew member is clearly visible on the floor holding a boom mic. The shadow even moves as the men walk away from the camera.
(at around 39 mins) When Norris and Mac climb down into the crater and are walking towards the open hatch in the center, look on the far right hand side of the screen and you will see the head and arm of somebody come into shot and then disappear again.
(at around 1h 15 mins) When the creature comes out of Norris's chest, there is a wide-shot with Mac in the foreground. In the air ducts on the ceiling, a crew members hand can be seen moving.
(at around 10 mins) On the "first day of winter" (June 21st) there is no daylight south of the Antarctic Circle.
MacReady states "I think it rips through your clothes when it takes you over." but there is no explanation as to how the newly 'born' duplicate replaces the victim's torn clothing. If the humans destroyed all clothing in the base (except for what they are wearing) any new mimics would be obvious. Alternatively, clothing is mimic-tissue, which would suggest that a duplicate couldn't take off any article of clothing (or if it could, whatever he removed would be 'alive', which would argue that any inanimate object in the base could be a Thing).
While burning the creatures might destroy the outside cells of what they were imitating, it would do nothing to destroy the cells on the interiors of the body. In fact, the body would act as an "insulator" protecting the inner cells from the excessive heat. Doc would have realized that and made mention of it.
(at around 48 mins) When the characters are burning the bodies of Bennings, the dog monster and the two-headed human, Blair is missing from the group for story purposes. But Clark is conspicuously absent, as well.
(at around 1h 6 mins) When Mac yells to Norris in the rec room, "Any of them move you fry 'em," a shadow cast by the crew's boom mic can be seen on the wall above Clark, Copper, and Garry on the couch.
(at around 58 mins) After MacReady asks if the blood test would have worked, it is seen twice above Kurt Russell's head.
(at around 1h 20 mins) Although Fuchs has told them that the alien organism is highly infective, they don't care about sharing the same knife to get their blood samples.
MacReady believes every part of the creature can act as a whole, and thus comes up with the "blood test" to determine who is The Thing. Despite this theory being proven correct, and even though he has a transitioning creature under control with the flame thrower, he inexplicably tosses a stick of dynamite onto the burning Thing after it's outside, blasting it into many smaller pieces, any one of which is potentially an individual creature.
(at around 1h 19 mins) During the blood test scene (before the Palmer reveal), even though there are other chairs available, Childs, Garry, and Palmer are tied up next to each other on the couch. Since the intent was to reveal the Thing without risking anyone uninfected, this move placed at least two of the men at undue risk as being so close to a revealed Thing could have resulted in their immediate infection.
(at around 1h 30 mins) When Mac, Garry and Nauls are underground, they split up and go alone to separate areas to plant the explosives. They do this instead of staying together despite knowing full well "The Thing" usually attacks a human while they're alone.
Despite the assessment that the all the physical matter connected to the Thing is part of its whole, an enormous amount of blood is left behind, which does nothing. In the blood test scene, it is clear that that blood is as much of the monster as anything else: it moves toward Palmer as he's mutating to escape. For the same reason, when the blood plasma bags are dumped into a pit to be burned, a character carries them with gloves and merely shakes off the excess. The gloves should have been burned as well.