Head scratches were practically law. It was a very little known fact -- and by little known that meant Sirius was basically the only person on the planet who knew -- that Remus loved a good head scratch too. Just behind the ear was the best spot ever.
It was still very surreal to him that he was sitting in a room with Sirius Black, doing The Thing and not the other thing that involved fighting and verbally slinging The Thing at each other like a weapon. He'd never imagined he'd find himself smiling again. Now here he was, bantering with Sirius and petting his hair. It shouldn't have been possible, but it was.
"Really, there's no way?" He teased. "Because that sounds quite like you, if I'm honest."