The Exact Moment Each Person Became Assimilated In The Thing

It seems incredibly strange to even suggest that MacReady was ever assimilated seeing as we see the majority of the movie through his eyes. However, as is detailed in full on the "Who Is Really Human At The Ending Of The Thing" video on ThatFilmTheory, there are moments when an infection COULD have happened.

After all, Nauls does find his clothes all torn up, and he does disappear for some time, during which he could well have been assimilated. However, the bigger question is: why?

Why doesn't he torch the others when he has the chance, why does Blair-Thing try to kill him, and why doesn't he kill Childs at the end?

Well, it's all to do with how The Thing operates. There's no suggestion that other variants of The Thing work together, all they want to do is survive whatever the cost and there's no camaraderie in that. Therefore it could well be that with a sabotaged blood test in which he took someone else's sample and focused all his efforts into playing the part, MacReady-Thing might well actually be a real aspect of the film.

Personally I find less weight in this as there's much more evidence to suggest the alternative, but still with a film this dense you need to consider every option.