[Right, that gets a laugh out of him. Not that it's hard to make Sirius laugh, but some are more genuine than others, and this one is definitely genuine.]

Ooh, you caught me. How did you know! [And taking this a little further, he adds:] Now, if you want any Remus bits, you'd have to shift into him. It's the only way you'd ever get anything.

[AND YOU DO WANT TO SEE REMUS BITS, DON'T YOU, but he doesn't add that. He only grins.]