He raised his eyebrows, waiting for James to admit to his injuries. The time for bravado wasn't whilst Sirius was trying to locate them. Sirius got down onto his knees and looked at the tear - it couldn't rightly be called a cut - on the back of James' leg. Sirius wasn't surprised that it was 'bothering' him, it was deep and Sirius could see the gleam of tissues he would rather not.
It was surprising that it hadn't bled more, but somehow injuries sustained in their animal forms were never as serious as those attained in human form. Fortunately neither of them had ever been faced with a transformed Remus whilst remaining humans themselves. Sirius could transform quickly, and had frequently left his change to the last moment, much to Remus' horror.
"Want something to bite on?" he asked, turning his face up towards James with the briefest of smiles.
Sirius' face straightened as he looked back down to the wound. It would need cleaning, and a couple of stitches to hold the edges together. "Deep breath in," Sirius instructed, raising his wand "and breathe out...now."
On James' release of breath he cast the cleansing spell over the wound, chanting the soft lilt of the words that took any infection away and any dead flesh. "Done," he said, looking up at him.