One design note that makes a periodic comeback is the "swallowtail" design, where a notch, often V-shaped, is cut out of the rear of the ski. This makes the tail into two independent fingers. When turning, only one edge of the ski is in contact with the snow, and in a traditional ski design, this pressure causes both the turning force as well as a torsional force on the ski, making it want to flatten out on the snow and lose the edge. The swallowtail allows the two tips to move independently, reducing this torsional force and, in theory, keeping the edge in firm contact.