In the film, veteran biologist Blair (A. Wilford Brimley) and doctor Copper (Richard Dysart) take a limited look at the mechanics of the Thing. “What we’re talking about here is an organism that mimics other life forms and mimics them perfectly,” says Blair. Each attacks, absorbs, and shapes itself as a carbon copy of its host, indistinguishable from its target. You don’t need a whole taxonomy classification to understand this; As Clark of Richard Masur said, “Whatever it is, it’s weird and annoying.”
The Thing cannot be detected unless it is compelled to reveal itself (the famous blood test scene) and several cast members questioned whether and when their characters knew they were infected. David Clennon, who plays assistant mechanic and resident stonemason Palmer, recalled hours of rehearsal time spent “discussing the metaphysics” about the infection:
“Some of the players were obsessed with the question: When you become the thing – when the alien takes over your mind and body – you know you’re Well? Or do you keep thinking that you’re just your ex? I couldn’t see the point of solving that silly riddle.”
Carpenter recalled that Russell was most insistent on this question. He told LA Weekly:
“The big question that kept coming to me was: If you were a Thing, would you know? I think Kurt Russell started it. I said, ‘I think you would’. But he kept asking that question, so I don’t think that answer is enough.”
This is an answer that Eric Vespe of /Film had in mind when researching the theory that MacReady was not only infected at one point, but knew about it. Dive down that rabbit hole Here.