well technically he already has by substituting rogue 2 for rogue 3 :b but on the vader shouts, this raises something that has always kinda bothered me, which is that it seems the "ompf" and the "ahh" noises should've been switched. The "ahh" sounds more like a noise you'd make if you got hit in the face with a bunch of steam (a sound of sudden and intense pain), and the "ompf" sounds more like the noise you'd make if you got knocked in the abdomen. After all, when Luke slashes his arm later in this fight and cuts his hand off in their next one, he howls out in pain, so obviously he can feel pain.