Hair removed from animal skin contains retrorse hair or fluff and must be treated before it can be used. For this reason, the hair is carefully combed several times and the tip of each hair is felt by the brushmaker’s fingertip to remove any unusable hair using a small knife called hansashi. This step can only be done by hand and the final brush must meet the vital sen-sei-en-ken criteria, that is, pointed and adequately arranged tip, while allowing easy drawing of circles yet the hairs do not break during the process.