Dr. Blair: 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.
Vance Norris: Finish what?
Dr. Blair: Finish imitating these dogs.
Dr. Blair: [throwing a fit in the radio room] You guys think I'M crazy! Well, that's fine! Most of ya don't know what's goin' on around here, but I'm damn well sure SOME of you do!
Childs: He got most of the chopper and the tractor, and he's killed the rest of the dogs.
MacReady: Garry, wait a minute, wait a minute. Now, Childs, go around to the map room door. Talk to him.
MacReady: Norris, get a table from the lab.
Dr. Blair: D'ya think that thing wanted to be an animal? No dogs make it a thousand miles through the cold! No, you don't understand! That thing wanted to be US! If a cell gets out, it could imitate everything on the FACE OF THE EARTH! AAAAND NOTHING can stop it!
Childs: Okay, Blair. Come on, man, you don't wanna hurt anybody.
Dr. Blair: I'LL KILL YOU!
I know I'm human. And if you were all these things, then you'd just attack me right now, so some of you are still human. This thing doesn't want to show itself, it wants to hide inside an imitation. It'll fight if it has to, but it's vulnerable out in the open. If it takes us over, then it has no more enemies, nobody left to kill it. And then it's won.