Clostridium tetani
There are reports of shuriken being coated with poison, intended either as a throwing weapon or to be left in a conspicuous place for a victim to pick up. Other reports indicate that shuriken may have been buried in dirt or animal feces and allowed to harbor the bacterium "Clostridium tetani"—if the point penetrated a victim deeply enough, the bacteria transferred into the wound could cause a then-incurable tetanus infection.