Its one of my favs, because although the guy is directing them for the first part of the shoot, when he says 'youre on your own now', you can totally see the women change intensity instantly, and go at it in a very competitive way, until one woman submits. It was actually a really hot moment when he said that, as you could see the mood change between the 2 women in a flash.
Its clear the director's idea for the shoot was to stage the first part to get the pics he wanted, but then have 2nd part with them catfighting competitively to get some real action shots. The models clearly agreed to this prior and knew what was going to happen (with the rules already laid out).
Its as though they were posing at first, with both just waiting for the green light to go at it for real. Then when he released them, all that bottled up energy that they were holding back when posing, just came out in both women instantly! Both were ready for it. I think when both models are competitive in nature, like these 2 women were, and they know they are being filmed catfighting competitively, neither wanted to lose on camera to the other women, as there is a lot of pride at stake. That's why it was so competitive I think.