Easter Egg: During the kennel scene, one of the Kennel Thing's tentacles hits it in the right eye. Then the head turns to the right and growls, before looking back at the men. It requires a frame-by-frame or .12 or slower DVD viewing to catch the tentacle striking the eye. This actually explains why the kennel thing turns to the side and growls, in the first place.
Charles Hallahan played his character, Norris, in some scenes, as suspecting himself of being the Thing, but not really sure. He's very much correct.
Another example, according to the commentary, occurs when Mac and Copper reveal the corpse of the Thing they recovered from the Norwegian camp. The production team used A&B smoke during the scene, with everyone gathering around. The cast's reaction to the stench is genuine.
Executive Meddling: An extremely bizarre example: the basic cable edit actually makes the movie a lot bleaker and nastier. Carpenter hates it for precisely this reason.
Improbable Age: The makeup effects, a landmark at the time and still very impressive, were done by Rob Bottin, who was only twenty-two at the time. Although Bottin did work for a year without giving himself a day off, often sleeping and eating on set and John Carpenter sent him to a hospital for exhaustion.
Re Cut: When airing on basic cable, the movie is naturally cut for extreme violence and to make room for commericials. However, a special re-cut was made for airings on TBS/TNT. Much gore was cut out - so much so that some deleted scenes were restored to fill out the running time. Additionally, there are opening and closing narrator sequences (the former providing exposition for the main characters and the latter running over an alternate ending).
Special Effects Failure: When Palmer-thing leaps onto the ceiling, you can see a part of the tile fly off the ceiling, and then stick back up onto it. This was because that part was filmed with him on the ground, and the film was simply transposed to make it look like he was attaching himself to the ceiling.
Whenever a tentacle wraps around something, it does so in an oddly rapid way. This is because all of the tentacle wraps were done in reverse.