Passing a Knot!
Occam Releasable Anchor
This was developed by my good buddy, Dave R. He is a canyoning maniac and this is a brilliant way to retrieve your rope(s) if you have to pass a knot during a rappel. Here, he uses some cheap lightweight, packable accessory cord and a wire gate carabiner.
It is advised to try any new skill under the supervision of a professional guide.