The 2 central questions of the plot - state your standpoint!
I think there are 2 crucial questions about the nature of the Thing, so I'd like to ask them, and then ask you to state your standpoint and back it up with evidence/arguments.
1. Does a Thing know that it is a Thing and not the dog/person/whatever anymore?
I wholeheartedly think that the answer is YES. My evidences are the following:
a) Someone got to the blood
This event does not make any sense if one of the imitations (either Palmer-thing or Norris-thing) did not anticipate that the group will devise a test to discover them. To stop this plan, they got to the blood. Simple as that.
b) Norris-thing's "heart attack"
This is IMO a diversion created by Norris-thing. He fakes a heart attack, but not because the thing imitated the faulty heart. The Thing does not even imitate all the internal organs, since that would not make any sense, it only needs to keep up the facade. It only needs to look like Norris from the outside (evidenced by the actual, revealed contents of his chest - there was no heart there at all!). So the imitation somehow gets the memories of the imitated person, and from that memory, it knew that Norris had a heart condition. It tried to "die" and make the group forget about the body. But they wouldn't leave it alone, shocking it with electricity even, and it did not like that, so it burst out, and we all know the rest. More on this in a separate thread here.
c) The internal logic of the film suffers, if Things don't know they are Things
If the imitations don't know that they are imitations, the whole internal logic and tension of the mind games and paranoia and all, and the infamous "The thinking man's horror film" alias goes out the window! I have always seen this story, even when I first saw the film at 11 years old, as a story of a group of people trying to outwit an unknown group of alien organisms who are trying to hide, and play mind games with the crew to separate some members from the group, devour them and imitate them. This is an intergalactic chess game, combined with a (or several) murder mystery (mysteries) and if the imitations don't know that they are imitations, then the multi-layered storytelling is simply not there anymore - and that would hurt the film.
2. Single cell "infection" theory - yay or nay?
I wholeheartedly think that single cell "infection" is NOT possible - the Thing is not a virus! Again, the logic and the thrill would go out the window the instant this theory is accepted, since Norris or Palmer only would have to scratch the skin of the others or drop a few drips of thing-fluid into their food or do some other BS like this and bam! - the humans stand no chance at all against something like that. Blair's animation is a bit misleading I think, and Fuchs' theory is just wrong. I don't mind that it was included in the film, but I think it is wrong.
How does it go instead of single cell infection? Well, I have always thought that the Thing needs a "critical mass" to be able to devour a victim. A dog-sized Thing can devour a human, and from then on, a human imitation of course can devour another human. But say that blood imitation in the dish MacReady used to bust Palmer, is still crawling around in the station - but can't devour anyone, since it does not have enough mass for that. So in my interpretation, the Thing attacks you, devours you, consumes you (this is the part where you are dead) and then imitates you. End of story, no infection and no "you" anymore, just a cold and calculating alien who wants to stay hidden and devour others.
This is of course my opinion, but I think I have backed it up with enough evidence and arguments. Now it's your turn: state your standpoint on these questions and let's hear your arguments!