 In short, many factors in the bitting equation must be considered to evaluate the action and severity of a bit.Various types of metal or synthetic substances are used for bit mouthpieces, which may determine how much a horse salivates or otherwise tolerates a bit; a horse having a moist mouth is considered more relaxed and responsive.Commonly used metals include stainless steel and nickel alloys, which generally do not rust and have a neutral effect on salivation; sweet iron, aurigan and copper, which generally tend to encourage salivation; and aluminum, which is considered drying and is discouraged as a mouthpiece metal.