Sirius jumps a little, not expecting the sound. He doesn't see any reason for the kid in the spectacular costume to be upset though. Maybe he knows the person he turned into? Figures a relative of Severus' would piss off a lot of people.

"What's your problem?" He asks in the most snarky voice he can muster. He's glad he at least kept the same voice. He would hate to think what the voice would have sounded like otherwise.