 Copper, aurigan and sweet iron (cold rolled steel) are incorporated into some bits to encourage salivation in the mouth of the horse, which encourages a softer mouth and more relaxed jaw.Bits also can be made of other materials such as rubber or plastic, sometimes in combination with metals.Throughout history, the need for control of horses in warfare drove extensive innovation in bit design, producing a variety of prototypes and styles over the centuries, from Ancient Greece into modern-day use.