>Thing, and MacReady is indeed having that conversation with a being that doesn't even understand what a noose is. Brilliant to create that kind of ambiguity.

Given the way the other characters that have been replaced act it seems that the Thing also acquires the knowledge of whatever it assimilates. (Otherwise it couldn't perfectly imitate the behaviour to fool the others). So if Blair was The Thing at that point it knew what a noose was. And if it's still just Blair then him ignoring it still makes sense. So a thing imitating him and ignoring it wouldn't be giving itself away since its consistent with Blair's previous behaviour.