Hate to bust your bubble but,= Knife Edge spins are a long way from being the hardest to do. In fact they are one of the easiest of the more complex aerobatics. It all comes down to stick motion with very little "feel" needed for the move. IMO the hardest 3D moves are (in no particular order) 1. Harrier rolling figure 8 with a reversal of roll direction at the cross over. 2. Crazy Ivan (aka Harrier rolling loop) 3. Using transitions from move to move.