Something about that grin reminds Castiel of Dean, and immediately he is on his guard and looking at House with increasing skepticism. He tries to pin the source of the problem, scanning House with a critical eye, before he settles back on the arm that had caused House's attention to drift, if even briefly.
He steps forward and without preamble, grabs House's arm at the wrist and pulls back the jacket's sleeve to reveal the jagged cut. He feels a swell of anger amongst his grace and piercingly gazes at House. "What happened?"