Japanese sais were farm impliments used to measure grooves in the process of planting seeds. They also doubled as defensive weapons used against sword-wielders. One skilled in the use of the sai could easily catch an enemy sword blade between the prongs of the sai and with a quick twist of the wrist...break the swords blade. They also were utilized as both thrusting and striking weapons, as well as a defensive protection for the arm. Sais help increase dexterity and knife-handling ability, and are often used as a practice weapon because of this.