Interesting fact:

Summer Glau (River) is a trained dancer. She used her dancing skills to shoot fighting sequences in ‘Serenity’. But she wasn’t the only one who got to perform stunts by herself. Mal and the Operative did not use stunt doubles during their fight, even though as a rule, there should be one actor and a stunt double. In that case, Joss Whedon maintained that “Nathan can take a punch in an almost extraordinary fashion”.