Sirius didn't blame him for keeping that a secret, of course. Some things were just not for other people, and the power of the head-scratching was strong. It was best not to let it be used for evil. Or, well, Sirius liked having things that were just secrets between them. He'd seek out head scratches from just about anywhere, but Sirius very much did not care for the idea of Remus doing the same.
The Thing was very much better when it was being used for good, and even a few days later after Sirius had turned the concept of everything that had happened around in his head, he was a little ashamed of himself for that. For turning against Remus because of his own bitterness and inability to be the one person his friend trusted best. He wasn't proud, and it wasn't even something he'd technically done yet.
"It sounds a little like me," he admitted. "A younger, more demanding version of me. But I'm not convinced."