- "I don't know who to trust."
- ― Blair to MacReady
During the winter of 1982, the Norwegians were chasing an Alaskan Malamute around the outpost, the pilot was killed when he accidentally dropped a grenade and the passenger was killed by Garry thinking that he was hostile, the crew adopted the dog. R.J. MacReady and Copper found evidence that the Norwegians had dug something out of the ice, the pair return to the station with the partially-burned remains of a hideous creature which bears some human features. An autopsy of the cadaver by Blair is inconclusive, save to find that the creature had what appeared to be a normal set of human internal organs. During the night, he was woken up by the fire alarm that was turned on by MacReady, he saw an unknown creature assimilating the dogs, MacReady ordered Childs to bring the flamethrower and ordered him to incinerate it. A subsequent autopsy by Blair reveals that the stray dog was an alien capable of absorbing and perfectly imitating other life-forms. Realizing the implications of this, Blair quickly becomes withdrawn and suspicious of the others.
Discovering that all life on Earth would be assimilated in just over three years if the creature were to reach another continent, Blair suffers a total mental breakdown, he began destroying the helicopters, tractor and radio with an axe, and killing the remaining sled dogs, containing further contamination. The team overpowers him and locks him in the tool shed. MacReady and the others later check on Blair, who is having canned food for dinner and seems to prepare to hang himself with a noose, he stated that he is fine now and wanted to go back to the outpost. Not taking any chances, MacReady still left Blair locked in the shed. Blair was eventually assimilated by the Thing and secretly constructs a small UFO underneath the shed where it plans to sleep through the winter until the rescue team arrives. The surviving crew set out to the tool shed in order to administer the test to Blair, only to find that he has escaped by tunneling his way underground. After the burning of the Palmer-Thing, the team was too late to realize that the thing got to Blair first *(somehow). Realizing that the creature now wants to freeze again so a future rescue team will find it, the remaining crew acknowledges that they will not survive and set about destroying the facility in hopes of killing the creature. While setting explosives in the underground generator room, the Blair-Thing kills and assimilates Garry, but it is unknown what happens to Nauls. It then mutates into a large creature. It emerges from the floor and then faced MacReady, who manages to throw a stick of dynamite at it, destroying the outpost and the creature in the process.
- There has been a debate among fans whether or not that Blair's computer program's projection on the Thing is actually accurate since it certainly isn't accurate in the sense that a biologist would not be working on computer animations as part of his investigations, especially under the pressing circumstances like we see in the film. This scene is obviously meant to be an aid to the audience to understand the Thing's life-cycle, not a realistic portrayal of a biologist's studies.
And how well does the simulation work, unfortunately, it leads to more questions than answers. We see dog cells being devoured, one by one, by a single Thing cell and this seems to contradict what we've already seen of the Thing's behaviour. Never does the simulation show that the Thing cells divide to replace canine cells, which is what would make more sense. So, the animation should be taken with a grain of salt.
On the DVD commentary track, Carpenter comments that they "didn't get it quite right" regarding the Thing's life cycle but that "it doesn't matter." From this it may be concluded that the goal with the computer sequence was not truly accomplished, so it must therefore be regarded with scepticism.
It's clear that the Blair computer simulation was meant to replace a similar scene in the script and novel. Alan Dean Foster's description of the Thing's cells seems to be better:
"Fuchs was preparing new slides, which Blair studied under the microscope. Two cells were visible through the eyepiece. They were active, neither quiescent nor dead. One looked quite normal. Its companion looked anything but".
"At the moment the two were joined together by a thin stream of protoplasm. Material from the larger cell, which was long and thin, flowed into the smaller, spherical cell. As it did so the smaller cell swelled visibly, until the cell wall fractured in three places. Immediately the smaller cell assumed a flattened shape like the other and three new streams of material began to flow outward from its interior. Neither cell appeared to have lost any mass."
"Blair pulled away from the eyepiece and frowned as he checked his watch. It was running in stopwatch mode. He turned it off. The resulting readout was very puzzling."
- The exact point when Blair was assimilated by The Thing is left deliberately unclear, and has been a source of open-ended discussion among fans.
- Scenario 1 - It is possible that Blair was assimilated by the Dog-Thing the first night it was on the base. Therefore, Blair was already an imitation when he sabotaged the vehicles, killed the other dogs, and destroyed the radio. With his "parts", both bio-mass and mechanical.
- Suggesting that it was the Kennel-Thing, When the monster separated itself just moments before it was incinerated by Childs, the Creature may have crawled its way into Blairs shed, Simply through the Front door regardless of what form or shape it took, Or underneath the Shed where it constructed the UFO. Highly Suggesting the front door since it was stated that it was open from that side.
- Scenario 2 - Blair was infected at some point by Norris or Palmer, when he was locked in the tool shed. This probably would have occurred during the hour-long blackout when a fuse was blown (probably by the Norris-Thing) and Fuchs died. Even in this case, it isn't clear if Blair is human or not in the scene when MacReady asks if he has seen Fuchs, and he asks to be let out.
- Scenario 3 - Though the likelihood is low, considering he wore gloves, during Blair's autopsies on the Norwegian body (deleted scene when he explains it isn't dead yet) and the dog with lobster legs he broke off.
- Many of the hard-core fans have pointed out over the years (much to Carpenter's rebuttal) that as soon as Blair's lips touched the tip of the eraser that made contact with the Kennel-Thing, during his report the cells had already begun assimilating and slowly spreading throughout him. Carpenter maintains that this wasn't in the script nor was it his intention, and is just an accident made by the actor. Others claim that even if this actually "happened" in-universe, it wasn't sufficient enough to cause takeover. However, if this were the case, he (much like Norris may have, when refusing leadership) felt himself being assimilated by The Thing and what was left of his humanity went berserk. Even imitating his rant (from the deleted scene) of no one getting off of Antarctica alive when he ambushed Garry.
- However, it no longer needed his eyeglasses and obviously constructed a mock-up UFO. While Fuchs does speculate that even a few cells can infect someone, it is also emphasised that assimilation is a violent and painful process requiring prolonged and close physical contact. If The Thing could infect with only a few cells, the Norris and Palmer Things would have infected Garry, Doc, and Clark when they tied them up, or even other characters through a seemingly innocuous tap on the skin (i.e. Norris is seen making direct skin-contact with Copper when he's tying him up along with Garry and Clark, but all three men were later revealed as human. This inability is also confirmed in the prequel movie where Colin was not infected by the unconscious Edvard-Thing although he was in direct contact with it for a half of minute at least.) It was possible he was infected shortly after he viewed the simulation of the things attacks, as his shirt changes from yellow to white, indicating his shirt was ripped when he was infected.
- There is one more possibility as to how Blair may have become infected. As we see the Blair-Thing towards the end of the movie, we notice the chest opening and a Dog-Thing emerges. It wouldn't have made much sense for the Thing to take on a form of a DOG, while it was in the form of a human host. One possibility as to how this came about was when TWO dogs escaped the kennel once Clark opened the gate. It is likely they would have been infected once the Thing had emerged. It seems logical that one of the dogs may have found Fuchs, otherwise it wold be unclear as to how and why Fuchs killed himself to prevent assimilation. That same dog may possibly have found Blair and assimilated him. The second one may possibly have been the one that was killed by Blair following the incident in the kennel. However, it was clearly stated that Blair had killed the remaining DOG(s) plural, and there were only two that survived the initial attack, so this theory is really all but irrelevant.
- It is unknown if Blair is a Thing when he asks Mac if he can come inside, as Blair was the one who constructed the UFO. He may have wanted free reign around the outpost in case he was spotted, or it may have been that he was still human and only wanted to go inside. It is also likely that if he WAS let back inside, they would notice that he was missing whilst he was collecting parts for the UFO. It is very possible and likely, that Palmer or Norris opened the door for Blair when they assimilated him, but the door would have to be locked from the outside, and Mac may have noticed if it wasn't when he went to see Blair whilst looking for Fuchs.