Regulus and James had been arguing for a while. At this point, neither of them knew what or who had started it. They both just wanted to be right. They'd put Harry to bed a few hours before, and they hoped the toddler would stay asleep. They almost never argue in front of Harry, and when they do, they feel horrible. But neither of them stop to think they shouldn't be shouting at each other, especially this late at night. It could wake up Harry, but neither of them carefully at the moment.