system
Given the following post, respond as if you're commenting on Reddit:
human
[The Thing] Why didn't the Thing assimilate Clark when it was alone with him for over an hour?
gpt
In the book it did. Clark was the first assimilated and then the first to be outed as a Thing and electrocuted. Like the other dozen or so Things he wasn't important, the only one who was was Blair. In the movie there are less people and Clark is still immediately cast into suspicion because of the time he spent alone with the dog. The reason it didn't assimilate Clark might be because it knew that instance of itself would be almost guaranteed to die. Palmer and Norris were allowed to operate with a lot of agency (relatively speaking) while everyone was suspicious of Clark. He ended up serving a much better role as a decoy than another pair of hands.

Tl;dr: The Thing has a self-preservation instinct and Clark would've been a liability.