I do not own Harry Potter. Shocking, isn't it?
Dancing, Sirius mused, was rather similar to dueling. Minus the various curses and hexes, of course.
When he was young, his mother had made him and Regulus take dance lessons. It was important, she had said, for young purebloods to know how to dance. Imagine the scandal that would result if a Black were to be at a ball, or some unimportant Ministry function, and couldn't dance.
So Sirius and his brother had learned how to dance. When Regulus was just four, and Sirius was six, their mother had hired a private dance instructor for them. They both took dance instruction until they started attending Hogwarts. Then, slightly later in their Hogwarts years, they were expected to go to various balls held by other prominent pureblood families, and the occasional Ministry function and dance with all the eligible pureblood girls.
By the time Sirius was twelve, dancing was second nature to him. He could go for a year without dancing at all, and then perform a perfect waltz. Provided he had a decent partner, of course.
After Hogwarts, when he had started getting into real fights, he had recognized that dance had value outside of political gatherings. As he had desperately tried to dodge curses in his first real fight, he had found his movements becoming more fluid. He turned and twirled and leaped out of the path of the spells sent at him.
He started laughing when, in the middle of the duel, he realized that he was dancing. His mother had been right. It was important to know how to dance. The years of training had given Sirius an edge many did not possess. His body was supple and quick, he could dodge spells with ease and not have to waste energy on countering or blocking all of them.
Watching a curse from his dear cousin Bellatrix shoot past him and hit the veil that had been behind him, Sirius laughed. What, he wondered, would his mother think if she knew his reasons for finally deciding dance was important?
Sending a flurry of spells at Bellatrix, he thought that maybe Walburga had known how he would end up using his dancing lessons. As he sneered disdainfully at his cousin, now bound by a non-verbal Incarcerous she had failed to block, he decided that his mother probably had known. She always had been exceptionally tricky, even for a Black.