Apparently, that thing lying on the table near Remus' bed, that thing with the handle and the wheel, was just too interesting for Sirius to resist.
"What's this?"
"That, Padfoot, would be a fabric cutter. Now put it down before you accidentally cut yourself."
"Oh, I won't. I'm not a child, you know...oh, it spins! Hey, wait, why do you have a fabric cutter?"
Remus sighed. "It's for when I sew. And yes… wheels tend to do that. That spinning thing. Agh! Don't spin it with your finger! You'll cut yourself!'
"No I won't…how sharp is it?"
"Sharp enough to cut you if you keep that up."
"Oh, I doubt it…" Sirius put the blade to the tip of his middle finger and lightly slashed. Nothing. "See, moony? No harm done." He did it again, to prove his point. Again, nothing.
Now contented with the fact that he was invincible, he began to do it over and over, with Remus watching apprehensively in the background. 'Padfoot, you're going to hurt yourself. Stop that.'
'You know, I really never took you for a sew-er. I mean, that's kind of really...poufy, even for you. And I think I would know just how poufy you really- OW! OW OW FUCKING OUCH!' Sirius dropped to the floor holding the injured finger in his mouth.
'I told you! I told you! What happened? Let me see it.'
'Nooo!' was the anguished howl of a reply. "It huuurts!"
"Oh just let me…" Remus gave up on trying to persuade him, and straddled him on the floor. That shut him up quite quickly. Note to self…
Sirius blinked. 'Remus?'
Taking his chance, Remus grabbed the injured hand to inspect the wound. 'Oh honestly now, Sirius, it isn't that bad.'
"Pain…agony…'
Remus snorted. 'Come now… you're fine, it's only a little blood.'
'Oh, misery…pain…' Sirius flung his hand up dramatically to his forehead and fluttered his eyelashes weakly. 'Death.'
All that merited from the werewolf was a raised eyebrow. He took the bleeding finger, licked it once…and bit.
'AH! DEATHDEATHDEATHDEATHDEATHDEATH!'