Ryuk found humans intensely interesting. And THIS particular human had made a fascinating decision, something that Ryuk found quite intriguing.
His legs crossed, it appeared that he was sitting upside-down in the middle of the air, head tilted at the white-haired human that seemed to be ignoring him, at the moment. He KNEW that Near could see him, so why he wasn't paying attention to him baffled the Shinigami; he was very entertaining, after all.
"You know, I'm surprised you KEPT that thing," Ryuk commented, moving from his upside-down position to perch near the Death Note on the desk. "I would have thought after the whole Kira fiasco, that would be the LAST thing you'd want." Maybe if he kept talking to him, he'd pay attention to him, something, ANYTHING to keep him from being so BORED.