Disclaimer: Duh.
For minutes B.J. and Murasame exchanged blows. B.J. masterfully evaded all of Murasame's aggressive strikes by just a hair. Finally B.J. used a hand on Murasame's arm to guide the force of his last attempted blow aside and off balance. Then he brought the knife down exactly as was called for in the script.
"Cut!" the shocked director yelled.
Ren turned to Murasame and said:
"Even if there's no choreography, even if you come at me with all you have, I can manipulate the fight so that it goes in the right direction for the show, without either of us getting hurt. That's the difference between our levels of skill."