I took him to the utility room where we got a tripe stick, came back and started talking to Mark - I was still holding the tripe. Duke, still ignoring the cats, barges and rubs up against me to ask for his tripe. Then he does a perfect 'sit' to ask nicely!
I took the muzzle off - still on lead, but no interest in the cats - gave him the tripe stick and he ate it on the floor in between Yama Bungle on the sofa and Suma Bungle on the footstool. Ate the whole thing without looking up, then sniffed all over the cushion looking for crumbs. Then walked out of the room with me.
Am trying not to get overconfident.