Not entirely related to wuxia fiction but i'm sure most of you have heard about this fearsome weapon:
"The Flying Guillotine" - the weapon is flung through the air and lands on the target, completely covering the victim's head. The assailant then pulls an attached chain, activating three blades that slice through the target's neck. The guillotine then sails back with the quarry's head secured inside.
There had been an old movie made about the flying guillotine but has this unconventional weapon ever appeared in Jin Yong or Gu Long (or any other wuxia authors) novels?
A note on the side: just saw a documentary on National Geographic featuring fearsome ancient chinese weapons and the flying guillotine is ranked number One. There are no actual historical records of the weapon but they made a working model of it and it actually works. They hired acrobats to test the model out and it is physically possible to somersault over someone and loop the guillotine over his head. Quite interesting.