Keening (3.5e Equipment)
From D&D Wiki
This property can only be applied to ranged weapons or ammunition. A fired keening weapon emits a high-pitched keen, forcing all enemies of its wielder within 20 ft of its path to succeed a DC 16 Will save or become panicked for 1 minute. If cornered a panicked creature begins to cower. If any Will saves succeed, those enemies become shaken for one round. This is a mind-affecting fear effect. Bows, crossbow and slings so crafted bestow the keening ability upon their ammunition.