Pack of ten.-Tetsu-bishi (also known as caltrops) are small metal weapons shaped so that one point is always up. They, like the shuriken, were a weapon used for distraction while fleeing. The ninja would scatter the caltrops behind them and anyone unlucky enough to step on them would not likely continue with the pursuit. They could also be thrown, and dipped in poison like the shuriken.
Pack of 10