Kunai knife is a Japanese tool that has a wooden or metal shaft and a curved, ridged "blade" secured by riveting. They were used as one of various hand-to-hand tools in ancient Japan and are still in use today.  The Kunai is a type of tool called an insertion knife, which has the blade set into the shaft so the weapon could be brought to bear inside an enemy's body with minimal risk of injury due to entanglement. The blades can vary from 8 inches (20 centimeters), commonly known as a "shuriken," to 18 inches (46 cm) in length, known as tanto kunai or shuriken tanto. What makes Kunai Unique? The kunai is a unique creation. One side of the knife blade is serrated, while the other side is smooth. It can be used as a survival knife and also as an improvised self defense tool. The kunai has been described by Robert Stroud (a convicted murderer in Alcatraz) as "the most menacing looking little devil" he has ever seen. Kunai is such a beautiful knife