I have been told a lot of contradicting things about the walk or standing or perhaps I get told what I'd supposed to do but it's seems mechanically impossible. A member had shown this video as a breakdown of the back walk. At 2:08 it says to bend the standing leg to make the movement smoother. It looks like she is bending her standing leg then stepping backwards to straight knees again. I'm confused now, every tango teacher has always said that your torso should not 'go up and down' and that the knees should be straight when standing... ok, so... clearly in the video she is 'bobbing up and down' because it is impossible to bend your standing leg to step and then stand feet together on straight knees without a little bit of the up and down movement. Are you supposed to always keep a slight bend in both knees while standing? Is it one of those things where they tell you that you want to eliminate the bobbing but it's more of a "keep in the back of your mind as a feeling" rather than something you ACTUALLY do?