Isuya

The isuya [強才; いすや] is a type of Kantonese arrow used by priests and warriors of feudal times. They were arrows which whistled when shot, and were used in both ritual archery and before or during battles. Isuya could also be used in expeditions or hunting parties as a way to signal for help; they are sometimes called tasuke-ya ['aid-arrows'] for this reason.
The sound was created by attaching a special carved or perforated 'bulb' of deer horn or wood to the tip. The isuya, therefore, could not do much damage except by blunt, direct impact. In Kiren, the sound made by the whistling arrows in mid-flight was thought to ward off and scatter evil spirits, who were disturbed by the high-pitched noise. Isuya were often used in purification rituals. There are records of the arrows being shot at buildings or people in order to symbolically and literally drive the evil out.
== Uses in battle ==
Isuya were most notably used during Kanton's feudal era in order to either start or finish a battle. After both sides had fired one isuya, the fighting was set in motion, and the defeated side was expected to fire another if they wished to retreat. Technically a battle was not considered truly over if a second arrow had not been fired to signal submission. Another use of whistle arrows was the delivery of messages, as rolls of paper could be easily attached to the shaft and launched over battlements or into enemy camps. It was also not uncommon for isuya to be used as distraction devices.
== Uses in religious ritual ==
Priests would fire isuya in order to instigate a purification rite. In some regions, and particularly in rituals conducted in the Imperial Court, a particularly skilled or famous archer would be summoned to carry out this task. The whistling arrow was considered vital in order to clear the surrounding area of evil spirits, who might interfere with the cleansing ritual otherwise. Starting in the 18th century, isuya were sometimes sold at temples as good luck charms, particularly around New Year. Simply carrying an isuya on one's person was considered auspicious and a ward against evil spirits.