Agreed, if Childs was, he wouldn't have just sat there.
Survival was the Thing's priority, not concern for saving humanity.
My password is a password.

I believe Childs wasn’t a Thing. If he was his main goal would have been to freeze itself somewhere in snow and wait for the rescue team to pick it up. Also Childs was still wearing an earring, and The Thing can’t replicate inorganic matter. And if we go by the 2002 videogame sequel which is said to be canon, then Childs did freeze to death while Macready escaped.

Wow good points. The movie seems scarier now. I think I'll watch it again soon.
Okay so what's your thoughts about the end? Was Childs a Thing?

Most likely explanation people go with is that Palmer sabotaged the blood sometime after scooping up the keys when Windows dropped them. Another possibility is that Palmer or Norris-Thing knew where a spare set of keys to the blood bank were. The Thing sabotaged the blood to prevent any further testing that would blow its cover.
As for Norris-Thing exhibiting chest problems, I think this was all an act in case anyone was watching it. The Thing is a perfect imitation in terms of behaviour and emotion. Mimicking the symptoms a man with coronary disease would only serve to cast away suspicion from it. Perhaps it was practicing in order to fake the heart attack.

It has been awhile since I have seen it…

1. Did we ever find out which one sabotaged the blood.
   I think Windows was carrying the keys to the blood fridge and dropped them.
   Who picked them up?
   Also, remind me please of how ruining the blood supply helps The Thing?
2. Then how do you explain Norris Thing having chest problems?
   Heart burn from digesting Human Norris?
   "Please vote to preserve the unique character of Warren…" - Robert Duvall

Thanks for telling us