I would say they're very aware of it. I mean Blair was building an alien spacecraft with the purpose of escaping, not to mention sneaking up on Gary to infect him. Also, Palmer's facial expression before the blood testing scene is a dead giveaway that he's aware the jig is up.
How aware they are is interesting, considering how they turn into gross monsters when they get caught. Maybe it's a defense mechanism they can't turn off or something.
Yeah, it does seem to vary from character to character. Norris is an interesting case because his nervousness only foreshadows his heart attack, which goes against the Thing's instinct for concealment. There is no reason for a Thing to have a heart attack, and its decision to chew off Copper's arms is clearly a reaction to the defibrillator unit.
quoting Childs from the movie:
CHILDS
The fire's got the temperature way
up all over camp... won't last long
though.
They're basically in sub-zero temperatures the entire time. When the final scene starts, the flames are still quite high, so it couldn't have been more then a few minutes. As shown with Bennings, it takes at least a few minutes for it to change one into a Thing, potentially 5 to 10 minutes.Within the context of the film, it seems unlikely that The Thing would be in a position to very quickly infect MacReady, when he basically just (potentially completely) blew up The Thing in an explosion strong enough to destroy the entire facility.
If MacReady was actually infected since getting lost in the snow, why would he even bother coming back? If it weren't for his intervention, Norris-Thing and Palmer-Thing would have easily taken care of the rest of the crew. Think about it, MacReady was the one who suggested the idea of the blood test in the first place. What would he have to gain by ratting out his fellow Thing?
Childs makes the most sense as being the Thing, for the simple fact that we don't see him for the entire climax. Considering how sneaky Blair-Thing is, it's highly likely he just got infected when he was all alone.
Another factor of the Thing's nebulous nature is just how easily it can infect someone else. The only time we actually see the Thing visibly assimilating a person is Bennings (you could also count the dogs in the kennel), and that's just because the two-faced corpse came back to life and started in on the deliberate, violent infection. If Blair's computer simulation is any indication (which, granted, it could very well not be), then it's possible that having any of the Thing's cells (which are all apparently autonomous right down to the slightest drop of blood if the test scene is any indication) enter one's body could cause the process to start from the inside and subtly take one over. You do make a good point about the ending, though the way that it is paced isn't an inconsiderable factor. We go from Mac throwing the dynamite and making a break for it, then the explosions that send the whole camp up in flames, and the next thing we know he's stumbled back to some other part of the base (and has apparently acquired a blanket in the process - from where? Who knows?).
There's also the question of whether or not other Things can consciously recognise each other as Things. At one point Mac states that he's human and that if everyone else was a Thing then they'd all attack him at the same time, which may or may not be true (him being human or Things being aware of each other or both). If the Thing's mission is self-preservation then it could very well be playing an elaborate chess game with the survivors (which is actually foreshadowed well by Mac playing computer chess at the beginning - his decision to pour whiskey on the computer and destroy it also foreshadows the fact that he would rather destroy the camp than "lose" to the Thing), such as having a secretly-infected Palmer point out the spider-head as it tries to escape.
To this end, an unwittingly infected Mac might be a pawn in the Thing's endgame. If Mac is already (unwittingly?) infected, then his plans actually work out surprisingly well for the Thing. Sure, Mac kills several Things over the course of the film, but if he's already infected then killing them off (aware of his nature as a Thing or not) is just a means to an end. His unintentionally causing the deaths of several other survivors still makes sense - and he can disguise it as him doing the best he can to fight the creature. It's his idea to do the blood test, which only adds to the theory that he can rig it, plus he ties all the suspects to the same couch so if a Thing is outed then it can kill other humans (as Palmer-thing does with Windows). Also, if Mac is already a Thing, then blowing up the base is the perfect way to preserve himself because it guarantees that any remaining humans will die of exposure while he/it can freeze as planned.
I've naturally considered the possibility that Childs is a Thing, and there is evidence to bear it out - the chief proponent is that the final scene is lit in such a way so that Mac's breath can be seen turning to ice in the air, whereas Childs' breath does not show up and implies that he is not actually breathing, therefore he isn't a Thing. Of course, that flies in the face of the idea that Things can replicate the humans perfectly. In any case, if Mac is infected then the fact that he decides to share his last bottle of whiskey with Childs at the very end could be seen as a deliberate attempt at infection (notice how, after Childs drinks from the bottle, Mac gives off a very satisfied little smile...)
For the purpose of argument I say we exclude the videogame and movie prequel. Only information provided by what's in the actual film should count, I'd say.
Yeah, especially when certain revelations from the prequel actually undercut the main film itself.