Draco couldn't really explain why he had just said that. When he took time to reflect upon it after the fact, he came up with a number of plausible-sounding reasons. Marge Dursley had been driving him nuts ever since he'd met her, talking about her country house like it was some kind of Malfoy Manor, when he was sure it was some little flea-bitten cottage in the middle of nowhere. By speaking disparagingly about Hogwarts, even under the cover identity of St. Brutus', she was unknowingly insulting Draco, and he had to stand up for himself and his school. Harry had been about to use magic in a very frightening and uncontrollable way, and Draco remembered the letter from Mafalda Hopkirk that morning and wanted to avoid further problems with the ministry. All those reasons were true and undoubtedly played some part in his action. But the truth was, he hadn't really thought about it at all. He'd just opened his mouth and the words came out, and now he had to figure out how to play out the hand.
Marge's jaw had just dropped open. Harry was looking stunned, but at least he'd gotten his magic back under control. Petunia and Dudley were looking frantic and giving him the throat-slashing gesture to tell him to shut up. And Vernon—Vernon was actually giggling in that nervous way he had, all too eager to brush off Draco's comment. "That's a good joke, Draco," he said. "Marge, I don't suppose you know what a prankster young Mr. Malfoy here is. Has us in stitches most of the time. Of course, he's not telling the truth. He's actually Dudley's friend and goes to Smeltings. Father is in the Ministry. Mother very high up in the social circle. He's a fine fellow. And what a sense of humor." He threw his arm expansively around Draco, who cringed inwardly at the overly familiar gesture at the same time he was thankful to be relieved of an explanation.
Dudley and Petunia started breathing again, Harry stalked off to his room, and the dinner resumed uneventfully. Without Harry there to goad, Marge and Vernon went back to being their usual boring selves, which was just fine with everyone else. After supper, they all went back to the living room and watched the telly until it was time for bed.
Now this was something Draco found fascinating. The telly was sort of like a moving portrait, the Wizarding Wireless Network, and a stage play all rolled into one. Miniaturized people moved around inside of a little box acting out a story, complete with sound. Periodically the scene would change and other little people would talk about why they loved their brand of orange juice or how much they wanted to take a holiday in Ibiza. It didn't take Draco too long to figure out that these interludes must be commercial advertisements. It was all rather distracting, especially the way the scene kept changing all at once without any explanation, but all the Dursleys loved it, especially Dudley. His favorite program of the evening was something called "Baywatch," involving scantily-clad young people who hung around by the seashore and regularly saved people from drowning. Draco supposed it made sense that Muggles would be poor swimmers, what with no gillyweed or bubblehead charms. But he didn't understand why so many people would keep getting in the water if they didn't know how to swim.
Finally Vernon turned off the telly (which involved pointing a long black thing rather like a wand at it) and announced that it was time for bed. Draco was the first one up the stairs and was just opening the door to his room when Petunia stopped him. "I guess we forgot to mention to you that Aunt Marge will be sleeping in that room tonight, Draco. We've moved all your things into Dudley's room. You'll be sharing with him." It took all Draco's willpower not to apparate back to Malfoy Manor.