Bent vs. Flexed Knees in Tango

Len Goodman made a good point that I was ready to present to students last night.
The video personnel caught Kurt Warner's choppy movement for us, and he was bummed out. He and Anna, who I like, got to bicker on camera about whose fault it was. As she recalled, he was having a hard time keeping his knees from straightening, so she didn't go into the difference between "bent" and "flexed" which is a matter of ease. Dancing should look easy and graceful.
A look of confidence should be conveyed by an upright head, not a hunched protect-the-neck position as is useful on the football field, as Emmet Smith pointed out.
I do like how that program ends up relating the dance to life.