Originated in the Philippines, the butterfly knife is also known as a Balisong knife.
It is a blade most commonly used as a utility or self-defense knife and the knife folds so that the blade is easily covered when closing the handles around it. Some people use it to make tricks, like spinning and flipping, called Fanning.
Other than these facts, the butterfly knife is pretty bad ass, and if you see someone carrying it, you can assume he probably knows how to use it, as it is illegal in many countries.
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