He searched for the sense of satisfaction he'd hoped to gleam from not only making Harry stagger but also from the trace of red blooming on his leg. He couldn't find it. There was nothing in him. No anger, no relief, no satisfaction. If it were possible, he felt emptier than he had after Disapparating away from Diagon Alley.
Because he wasn't really angry with Harry. Or if he was, it was nothing to the anger he felt towards himself.
So instead of taking advantage of Harry's brief distraction, he simply waited, wand near his side, for the next attack.