Childs has to be The Thing at the end..
There's many interesting theories out there wether Mac or Childs is the Thing and the ending is shot like that on purpose which makes it a great film. The one conclusion I came to it being Childs was the script. I seriously doubt the filmakers said "ok, you're gonna play Childs. This character toward the end of the movie, you're gonna go outside cause you thought you saw somebody walking outside, then disappear for a while and come in at the end of the closing shots. And that's all you're gonna do" His role has to be bigger than that at the end. I believe he is The Thing.
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