Plot hole: It's never explicitly stated or shown that the Thing reproduces with each victim until the movie is nearly over (when Palmer infects Windows). Most viewers figure it out from the context, but it's unclear just when and how the characters themselves have come to this conclusion. This was an inadvertent result of an editing decision and a visual goof: there is a deleted scene in which Blair explains much more directly that the Thing multiplies according to how many victims it takes, and in its place in the final film is a scene containing a computer simulation that director John Carpenter acknowledges was a failed attempt at explaining the organism's life cycle.
Suggested correction: This isn't a plot hole. It's explained in the computer scene that the entire world population would be infected 27,000 hours from first contact. That only makes sense if the organism reproduces. Even without that explanation, there's no plot hole. The plot still works. The characters come to a conclusion. They might have worked it out, guessed, or simply be wrong. Just because that's what they believe it doesn't make them correct.
True, it has "the effect" of a plot hole more than it literally is one in itself, but it's the closest category for a pretty unique expository failure for a major studio film; one confirmed to have been a total goof in the production. All we have for most of the film is the implication of the word "infect" going up against VERY clear and misleading exposition of the Thing's nature. I'll consider changing the type to "Other," but I feel strongly it should be represented.
Trivia: In the scene where Mac destroys Palmer with a stick of dynamite, the explosion was much bigger than Kurt Russell had been led to expect. Watch him closely as the explosion occurs. He flinches violently and nearly falls down. It's quite comical.
Suggested correction: I've just watched this scene having read this entry, and I don't see Mac / Kurt do anything other than is expected or appropriate for the scene. There's a big explosion and he almost falls backward. There's nothing comical about it.
Other mistake: When Doc uses a computer to watch/simulate dog cells being assimilated by a "thing" cell, we can see a single cell fusing with multiple dog cells to imitate them. This process would lead to the dog being digested until it remains only one cell, and not to the replacement of all of its cells by the imitators. (00:40:30 - 00:41:25)
Suggested correction: The computer simulation isn't showing just one cell taking over an entire dog, but showing how the creature can get the genetic makeup of whatever it touches and replicate it perfectly.
I think it's fair to consider this a goof. John Carpenter states on the director's commentary his goal through this sequence was to demonstrate the life cycle of the Thing, and acknowledges that the visual isn't accurate for that purpose.
Pretty much the entire rest of the movie unfolds as though the simulation showcased the Thing spreading / multiplying: it's followed by text saying the entire human population could become "infected" after a certain amount of time; it's not until after this scene that anyone besides Blair is worried that one or more of them has been taken over. It's a valid movie mistake because the movie itself seems to assume the audience saw something different than what was actually shown.
