With a little sound of dismay as he's conveyed so easily from one point to another, Benedict is briefly cowed, and has to take a moment to catch his breath once pressed against the tree.
The look he gives Gabranth now is one of sheer, purposeless impudence; on some level, perhaps closer to the surface than it appears, he knows the man is right. For this reason, he doesn't answer: doesn't disagree, doesn't tell him off or wish him gone.

It's a terrible impulse that drives him to be just as petty as possible, and that's why, for the last pathetic throe of his dying argument, he simply jabs his finger through the eyehole of Gabranth's helmet.
Take that.