Factual error: When the infected Palmer starts his transformation into the Thing, he has a series of fits and the creature 'falls', or leaps upward onto the ceiling. Watch closely...you can see a piece of paneling also 'fall' upward, when it should have fallen down. (01:23:20)
Factual error: In the kennel scene, MacReady fires at least 7 shots from a pump shotgun. That particular shotgun can only hold 5.
Factual error: At the beginning, MacReady dumps a tumbler of ice and scotch into his computer, which spews a shower of sparks as it shorts out. No electronic device, not even an old 1980s personal computer, sparks like that when shorted out. It simply goes dead.
Factual error: If you are at or near a pole, aka Antarctica, you either have 24-hour daylight, 24-hour night, or a kind of continual dusk-like condition. You don't have bright day and dark night at the same time.
Answer: At the end, the large creature presented itself as an amalgam of beings it had absorbed-part Blair, part dog, and various other beings with tentacles, insect-like legs, and a worm-like body. I don't believe that we really ever see what its true form is, if it has one.
Erik M.