quickly than can be delivered by the muscles, resulting in much higher velocity and, hence, greater distance. This same process is employed by frogs, which use elastic tendons to increase jumping distance. In archery, some energy dissipates through elastic hysteresis, reducing the overall amount released when the bow is shot. Of the remaining energy, some is dampened both by the limbs of the bow and the bowstring. Depending on the arrow's elasticity, some of the energy is also absorbed by compressing the arrow, primarily because the release of the bowstring is rarely in line with the arrow shaft, causing it to flex out to one side. This is because the bowstring accelerates faster than the archer's fingers can open, and consequently some sideways motion is imparted to the string, and hence arrow nock, as the power and speed of the bow pulls the string off the opening fingers. Even with a release aid mechanism some of this effect is usually experienced, since the string always accelerates faster than the retaining part of the mechanism. This makes the arrow oscillate in flight—its center flexing to one side and then the other repeatedly, gradually reducing as the arrow's flight proceeds. This is clearly visible in high-speed photography of arrows at discharge. A direct effect of these energy transfers can clearly be seen when dry firing. Dry firing refers to releasing the bowstring without a nocked arrow. Because there is no arrow to receive the stored potential energy, almost all the energy stays in the bow. Some have suggested that dry firing may cause physical damage to the bow, such as cracks and fractures—and because most bows are not specifically made to handle the high amounts of energy dry firing produces, should never be done. Modern arrows are made to a specified 'spine', or stiffness rating, to maintain matched flexing and hence accuracy of aim. This flexing can be a desirable feature, since, when the spine of the shaft is matched to the acceleration of the bow(string), the arrow bends or flexes around the bow and any arrow-rest, and consequently the arrow, and fletchings, have an un-impeded flight. This feature is known as the archer's paradox. It maintains accuracy, for if part of the arrow struck a glancing blow on discharge, some inconsistency would be present, and the excellent accuracy of modern equipment would not be achieved. The accurate flight of an arrow