People generally tend to focus on the blade on the front side of scissors, but it is the back edge that is the heart of the scissors and determines their sharpness. At first glance, the back side of the scissors appears perfectly flat, but in fact there is a "sawa" (a groove) toward the center, and the two blades interlock to cut. The cutting action requires that the tips of both blades rub against each other at a single point, which requires the back edge to be curved and sharpened by hand. The manual back sharpening process, which requires advanced craftsmanship, is a traditional technique of Toyama Blades that has been handed down for generations.