Butterfly Knife

A butterfly knife, also called a balisong, is a folding pocketknife whose two handles counter-rotate around the tang so that the blade is concealed within grooves in the handles when closed. The knife is closely associated with the Philippines, and its name comes from Barangay Balisong in Taal, Batangas, a historic center of knife manufacturing alongside the neighboring barangay of Pandayan. Mass production of the balisong can only be documented from the early 1900s, and while one theory traces an ancestor to a French measuring tool called the pied du roi, the modern form was developed and popularized in the Philippines, where it grew larger than that prototype and became used mainly as a weapon with quick-opening techniques developed for self-defense. A traditional balisong measured about 29 centimeters (11 inches) when open, earning it the Philippine nickname veinte y nueve, or twenty-nine. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/