What Happened?
What happened to the "arms" that came out of the Thing in the dogtown scene? You know, the ones that go through the ceiling? I always thought that they met up with Blair-Thing, and that is why in the end Blair-Thing is so large.

From memory we don't actually see what happened to them but we do see MacReady toasting the dogthing with the Flamethrower. We can only assume they were roasted. eeeccchhh barbequed dog hair :P

But the "arms" go through the roof BEFORE Dog-Thing gets torched (And it wasnt Mac that torched it).

The Spider-Thing
the arms or legs or whatever the heck it is...came out of the dogthing...went up the wooden ceiling...pulled itself out of the dogthing...then the dogthing along with the spiderthing got torched by childs....the spiderthing then fell back onto the ground...the spiderthing just couldnt hold on much longer...

So where did the arms go????

The "arms" meeting up with Blair-Thing makes sense because of the "dog" that comes out of the side of Blair-Thing.