It was obvious that Regulus was tired of waiting. He sat perfectly straight, fingers folded over each other. He'd even managed to grab a lazy smirk and hold onto it, support it, wear it for fifteen minutes.
Yet Sirius knew that underneath the image of a perfect Pureblood lurked a nervous wreck. Today Hogwarts acceptance letters were sent out. Of course Regulus would get in. Anything otherwise would be unacceptable. That pressure was what drove Regulus crazy.
The only comfort Sirius could give was to keep up the pretense he didn't give a crap.