stay underwater for longer periods of time. Goshiki-mai (go, five; shiki, color; mai, rice) colored (red, blue, yellow, black, purple) rice grains used, in a code system, and to make trails that could be followed later. Despite the large array of tools available to the ninja, the Bansenshukai warns one not to be overburdened with equipment, stating "a successful ninja is one who uses but one tool for multiple tasks". Weaponry Although shorter swords and daggers were used, the katana was probably the ninja's weapon of choice, and was sometimes carried on the back. The katana had several uses beyond normal combat. In dark places, the scabbard could be extended out of the sword, and used as a long probing device. The sword could also be laid against the wall, where the ninja could use the sword guard (tsuba) to gain a higher foothold. The katana could even be used as a device to stun enemies before attacking them, by putting a combination of red pepper, dirt or dust, and iron filings into the area near the top of the scabbard, so that as the sword was drawn the concoction would fly into the enemy's eyes, stunning him until a lethal blow could be made. While straight swords were used before the invention of the katana, there's no known historical information about the straight ninjatō pre-20th century. The first photograph of a ninjatō appeared in a booklet by Heishichirō Okuse in 1956. A replica of a ninjatō is on display at the Ninja Museum of Igaryu. An array of darts, spikes, knives, and sharp, star-shaped discs were known collectively as shuriken. While not exclusive to the ninja, they were an important part of the arsenal, where they could be thrown in any direction. Bows were used for sharpshooting, and some ninjas' bows were intentionally made smaller than the traditional yumi (longbow). The chain and sickle (kusarigama) was also used by the ninja. This weapon consisted of a weight on one end of a chain, and a sickle (kama) on the other. The weight was swung to injure or disable an opponent, and the sickle used to kill at close range. Explosives introduced from China were known in Japan by the time of the Mongol Invasions in the 13th century. Later, explosives such as hand-held bombs and grenades were adopted by the ninja. Soft-cased bombs were designed to release smoke or