A caltrop (also known as caltrap, galtrop, cheval trap, galthrap, galtrap, calthrop, crow's foot) is an antipersonnel weapon made up of two or more sharp nails or spines arranged in such a manner that one of them always points upward from a stable base. Caltrops serve to slow down the advance of horses and human troops.
Shinobi wouldn't normally scatter these randomly on the run but instead they were placed in areas where they could provide a passive defense. 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. They would also be placed under shallow waters in order to slow down samurai troops traveling through lakes and rivers.
The Giyoshu military manual recommends scattering caltrops or placing bamboo nails into the ground to prevent shinobi from infiltrating. Caltrops would also be attached together through rope. Sand or rice would also be scattered along the ground to identify footprints. Additionally, caltrops and spikes would also be used during ambushes and placed around tents.