Character mistake: The last time Doc tries the defibrillator on Norris, he uses it on the abdomen instead of on the chest. He also positions the pads incorrectly. They should be placed diagonal, with the heart in the middle, not horizontal.
Character mistake: When MacReady is giving the blood test, the scalpel they are using is not properly sterilized after each person cuts themselves (shown when Nauls cuts himself, then when Windows goes next: all he does is wipe the scalpel on his pants). Using the same scalpel seems like an extremely stupid thing to do as Fuchs told MacReady that even a small particle of the Thing could take over a person. (01:19:55)
Character mistake: The spaceship is much deeper in the ice than frozen thing, indicating it was buried a hundred thousand years after the spaceship landed. Norris' calculation of the age of the spaceship wouldn't apply to the thing, which was hardly buried at all, by comparison.
Answer: Remember that he'd just spent the whole day investigating how something mysterious and horrible destroyed the Norwegian camp, so he's already in a spooked state of mind. Hearing the dogs screaming at night is already unusual on its own, and also reminds him how this whole episode all started with a crazed Norwegian trying to kill a dog. Deep down he knows whatever happened to the Norwegians is now starting at their own camp.
TonyPH
I 100% agree.