Sirius' language was a bit stronger than Dorcas' as he rebounded off the Ravenclaw girl. In the meantime, the cat she was holding appeared to have some kind of hissy fit, where it attempted to cause phsyical harm to everyone within ten feet of its person. The animal lashed out and dashed away, making Mrs Norris look almost peaceful, and leaving Sirius gazing a little blankly after it.
In the second of their rather spectacular collison, Sirius had recognised Dorcas Meadowes - they were in the same year and had a few classes together. "Oops." He turned again to watch the cat vanish round the corner. "Sorry about that, Meadowes. But you should really stop creeping around corridors, you know."
Sirius pushed long hair back from his forehead and flashed her his infamous grin. It faltered a little, however, when he noticed the way she was clutching at one hand. He winced a little, stepping forward. "Blimey. You alright there?"