Look Ma! No hands!

I was struck at class last night by how comfortable we become in doing certain poses, even when we believe we are challenging ourselves. Last night, we were asked to place our hands in namasgar (reverse namaste), and i was amazed how many problems that created for me. Our instructor explained the importance of removing the hands from the practice of the pose to continue to challenge ourselves and focus on different parts of the body in balance. I fell out of the pose a couple times and had to use my hands to catch myself, but it was an eye-opening experience to see how much we rely on hands/arms even in a pose like Virabhadrasana II, when the focus is on the legs, hips, spine. Are there small things you've been asked to do that changed your perspective on a pose, or shifted your attention to a new area?