Sirius froze, both at Remus's unexpected advance- he was usually the arsehole who pushed and wouldn't leave well-enough alone, except of course near the full moon, which this was, so maybe he shouldn't have been surprised- and at the words. He couldn't quite rationalize interpreting them as a joke, or even responding with one, even though that would certainly have been the safer thing to do.
"Are you?" he asked after a moment, low, not denying the first bit because that would have been an outright lie and just about everyone knew it. So much for dignity after all.