Blood circle

In Boy Scout parlance, when holding a knife the area within the radius of the arm and blade length combined is called the blood circle (or safety circle in contemporary use). This area can be envisioned as a hemisphere with a person and a sharp instrument at its centre. In one example, an area within the radius of the arm and the blade length of a knife combined is an area where the intended or unintended meeting of steel and flesh would cause blood to flow.

It can also be seen that the backswing of an axe would cause considerable damage to a person unlucky enough to come in contact with the instrument during its journey through the arc of the swing.