Created in Southern China, the Butterfly Sword (often seen as a set of two swords) dates back to the early 1800s.
Background and Use
Butterfly swords were originally created for easy hiding in sleeves, boots, packages or other easy ways of transport, making it possible to spring a surprise attack and/or carry concealed weapons for protection. Sometimes the owner will also put both swords in a single scabbard, making it seem as though they are only carrying one single sword.
The sword is normally sharpened on only one edge, and only half of that edge - from the end of the blade until about half way down. That way, the sharper top end of the blade can be used for slicing and cutting, whereas the lower unsharpened half can be used for non-lethal (but still damaging) blows, without corrupting the sharp edge.
Most sets of swords are unique -- they were generally not mass produced in factories or by large workforces, but rather, created for individual martial artists.
Butterfly Swords (also known in English as butterfly knives) are often used in martial arts, regularly being considered an extension of open-handed combat, due to their size.
Historically, butterfly swords were also used by monks who preferred self-defence or to just damage their opponent without inflicting fatal blows.
Butterfly swords have been featured in the Teenage Mutant Ninja Turtles moves, as well as featured in the TV show Forged in Fire, where contestants were challenged to make a set of butterfly swords and then tested against a range of strength and sharpness tests: