This is inspiring for several different shots...one exactly like this with two girls falling the same direction. Both girls next to each other but with one girl a step back so they don't fall on top of one another obviously. This would show progression of motion if the girl in the backround began to fall first and would give a domino effect. Also if two were side by side each took a step foward and fell back. A profile shot would could made giving them a triangle geometry within the frame if caught at the right moment.