The Thing (1982) | John Carpenter

The story starts out in Antarctica, where a group of scientists is bunkered until one day they are disturbed by the sounds of gunshots coming from a Norwegian helicopter, apparently trying to kill a runaway dog.  They miss their quarry, and the Norwegians end up getting offed, with no explanation as to what their problem is.  Fearing more violence, the American crew travels to the Norwegian camp, only to find some very odd occurrences, including a mangled humanoid body that has normal internal organs.  Then, the dog reveals that it is not really a dog, but some sort of alien organism with the power to mimic other life-forms and dominate until it takes over everything around it.  The men of the camp are its next intended victims, and soon, no one can trust the others. Kurt Russell, Keith David, and Wilford Brimley appear. Directed by John Carpenter.