makibishi

The term refers to small, spiked caltrops used by ninja to deter pursuit. When pursued by enemy soldiers, ninja would scatter makibishi on the ground. In ancient Japan, common footwear consisted of sandals made of straw, called zori, which offered relatively little protection against such hazards. Makibishi spines were often hooked, and occasionally grooved to allow for a light coat of poison, to increase the damage they dealt to those unfortunate enough to step on them and possibly result in death.
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