From The Thing
[showing the remains of the dog-thing to the entire camp
You see, what we're talkin' about here is an organism that imitates other life-forms, and it imitates 'em perfectly. When this thing attacked our dogs it tried to digest them... absorb them, and in the process shape its own cells to imitate them. This for instance. That's not dog. It's imitation. We got to it before it had time to finish.
Finish imitating these dogs.