Remus is attached to his possessions. There aren't very many of them, and it's rare that any are ever added to the collection, but what he has...well, it belongs to him.
Oddly, Sirius, who never used to understand other people's boundaries, seems to get this. Because when Remus leaves his things in the room he sometimes crashes in at number 12, everything's always in the same place that it was before, and while Remus can smell the faint scent of Sirius' fingers (sadness and dirt that never quite washes clean and chocolate) there's never any more evidence that anything was touched than that.
There's one item that the smell is always stronger around, Remus's battered copy of The Wind and the Willows. His mum sent it with him to Hogwarts, sent it and the words, "Remember me at night, love," since that was always when she read to him from it, read to him with voices and a lilting pitch and everything that still, to this day, causes memories of her to rush back at him, mostly at a speed he can no longer handle.
Sirius doesn't leave the book carelessly open, or bend its pages, or do anything to upset Remus, but he obviously flips through it. At length. Remus wonders if he reads it. Remus wonders if he should suggest it. Might take Sirius's mind off of things. Might not.
Remus picks the book up and cradles it in the palm of his hand. He flips through the soft pages and allows them to settle where they will, reading at the passage closest to the top of the left page. The words wrap around his mind and for a moment, just a moment, where he has to go next, how Sirius is handling this latest confinement, what Voldemort may or may not be doing in Harry's head, none of that matters. A small smile presses at the corners of Remus's mouth.
He really does like this book.