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"Good. So Andromeda taught you the ceremonial forms, just in case you were unfortunate enough to be challenged." Or be like James and issue a challenge, Remus thought. "Now, in a tactical sense, a duel is basically a fight with rules. And there are more rules than you might think—a lot of them are usually implied, like 'Don't cast until the start is called', 'Stay inside the duelling area', and 'Only cast at your opponent.' More explicitly, the standard rules are, 'Don't kill or permanently injure your opponent', 'Don't physically touch your opponent', and 'Stop when your opponent is disarmed or incapacitated'. Mind you, in a real fight, none of these rules applies, although 'No Unforgivable Curses' still does.

"But I know that your natural style is quite a bit different from this, so we'll start there. Now, I'm sure that you quarrel at home from time to time?" he said wryly, looking to Dan and Emma.

The kids' parents nodded and rolled their eyes. Emma mouthed, "Ohhh, yes."

"Well, I'm about to give you a legitimate outlet for that. We're going to start this off the way you would do it at home—no wands. You may use wandless magic, or any kind of physical skills. Just don't cause any serious injuries on each other, alright?"

Harry and Hermione both nodded to Remus and then grinned evilly at each other. Magic was already crackling around their fingertips. During the week of cleaning, Sirius had moved everything he wanted to keep from the attic into his Gringotts vault and turned the space into a magical training room in which the children were now paced off, something that they would soon realised was a very good idea.

"I'll count you off—on three. One…two…three!"

The children sprang into action. While they had quarrelled and roughhoused in the past, they had never really had a chance to go all out at home. Hermione, being better with magic, shot off a precise volley of faintly glowing spells from her hands and tried to dance around Harry's clumsier spells. Since Harry's strength was karate, he was trying to close the distance between them, but it was difficult with so many of what looked like Stinging Jinxes in the air, along with the occasional streams of conjured sparks for distraction and something that didn't look like a proper spell, but was similar to a Flipendo,to try to knock him down.

Both of them were fast for their age—not professional level, but wandless spells were undoubtedly quicker to cast than wanded ones, and that fact that they were doing this wandlessly—and mostly wordlessly—was what made it look so dazzling to wizard eyes.

And they also had no way to disarm each other.

http://www.fanfiction.net/s/9863146/33/