This pic shows the tension created by pressing down on the chicken's lower jaw/beak that brings the skin taut. This knife position is for cutting across the entire neck, but nowadays I just cut the right side of the neck as it is positioned in the pic...but the left hand position is pretty much the same. In cutting the right side, the knife point is positioned towards me and I cut from near to far in a deep, decisive cut. Sort of like the knife position and cut one would make while whittling a piece of wood...
