Harry Potter looked into Draco's eyes, and saw that the blond was still fuming (Harry liked to consider himself an expert on suppressed anger. He'd been through a lot of it in his life - thanks to Snape, who never quite got up enough dungeon to strike*, but seemed to have no such issues with 'dark sarcasm' ).
Well, Harry'd had enough of himself shoving the anger down deep inside. He wasn't about to deal with Malfoy doing the same. "What's actually got you upset?" Harry said as he crossed his arms**.
"You didn't tell her?" Draco Malfoy said, gesticulating wildly - so much so that half his gestures seemed to impact Harry's chest. "I was watching you - Granger wouldn't not react to that." Draco continued gesticulating - hitting Harry's chest harder, until Harry actually stepped back. Which didn't work, as usual, because Malfoy got right up into Harry's personal space anyway. "Why didn't you tell her?" Draco snarled, inches away from Harry's face.
Harry smirked, channeling Fred, and said simply, "And let you miss out on all the fun?" Harry pulled his shoulders back (lifting his chest), "Tell me you didn't want to hear her reaction."
Draco Malfoy dismissed the rhetorical salvoy with a shake of his head. "You were just scared of telling her."
"Telling who what?" Hermione asked from the doorway.
Both boys jumped half a foot into the air, scrambling away from each other as they ... reacted.
"Nothing," Draco Malfoy said, in an attempt at nonchalance.
Harry Potter knew better - Hermione turned into a leech if you didn't tell her something and she found out about it. "Draco doesn't want to tell you about what Dumbledore discussed yesterday with us in his office."
Draco turned betrayed eyes that promised vengeance on Harry Potter. And then spoke up, "The barmy old fool-"
Hermione Granger never let anyone say anything mean about Snape; she wasn't going to let Dumbledore get insulted in his own school. "Draco Malfoy! How dare you speak about our illustrious Headmaster that way!"
"He's barmy and everyone knows it." Draco says, stuffing his hands in his pockets.
"He's intelligent, and wise, and very nice." Hermione said firmly.
"Oh, yes, how very good a nice person is." Draco Malfoy drawled. Harry Potter could believe in a 'good' Draco Malfoy, but a nice one? That was about as likely as Snape turning out to prefer wearing yellow***.
Harry saw something curious, as Draco Malfoy swallowed, and then spoke. So that is Malfoy when he's uncertain. Malfoy said, "Your wise Headmaster has decided that Potter and I need to be punished for our fight on the Quiddich Pitch."
Harry was a Gryffindor, and really didn't think it proper to just let Malfoy have to say everything. "As punishment, I'm going to apprentice with McGonagall."
"And I'm going to apprentice with Professor Snape." Malfoy said.
"Dumbledore comes up with the best punishments, doesn't he?" Ron said with a gormless grin. "The two strictest teachers in school!" Ever oblivious, Ron had missed the burgeoning energy building up in Hermione.
Unfortunately, Draco and Harry hadn't missed a single thing. Frozen like deer in headlights, they waited for the explosion.
**Harry doesn't realize how intense "Stubborn Harry" comes off as. He's used to being small and ignored, growth spurts aside.
***Yes, Snape would look absolutely awful in yellow.
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