It was, perhaps, a sign of his old age. He now could look out the window and sit in one place in quiet contemplation.
He could stop moving. Stop thinking. Just remember. Remember what it was like when he was younger. Like the Master. Previous companions. The end of the universe. Ah, the fun things to remember.
He never let himself think about these things when he was younger. Or maybe it was just being around River. Her home made him feel calm.