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The blood circle, also known as a safety circle, is a term used in Scouting to describe the area within the radius of the arm and blade length combined, when using a knife, saw or axe. This area can be envisioned as a sphere with a person and a sharp instrument at its center. Presumably, anyone within this radius is at risk of injury. To prevent injury to others, it is considered desirable to keep other people outside of the circle at all times. The practice of delimitating a blood circle is used for a number of activities involving sharp instruments, including whittling.