To prove I'm alive", Regulus replies, wincing slightly at the fact he's voiced it out loud. Sirius still looks lost, so he elaborates, "if I'm bleeding, then I'm not decomposing."
"Reggie, what the fuck?" Sirius replies, aghast. He really doesn't know how else to respond to that. "What the fuck happened to you? Why would you think you're fucking decomposing? You're not a banana peel in a compost bin."
Regulus blinks rapidly at Sirius and then says, "yes, I am aware."