This was all done last night after I scanned the sketch version, and I was still watching T2 while I worked. Looking at it now I suppose a background of some variety is in order, but the ideas aren't there for it yet.
Duke's arm is cybernetic, but that's the only part of him that is. He just usually has a sleeve of fake fur over it (currently torn off) so it looks more normal. He also never wears sleeveless shirts.