bit

"A bit is a type of horse tack used in equestrian activities, usually made of metal, or a synthetic material. It is placed in the mouth of a horse (or other equid) and assists a rider in communicating with the animal. It extends from one side of the mouth across to the other and rests on the bars of the mouth, which are a region, between the incisors and the molars, where there are no teeth. It is held on a horse´s head by means of a bridle and has reins attached for use by a rider.

A bit functions through the principle of negative reinforcement: the reduction or relaxation of pressure as reinforcement for a behavior. The rider applies pressure through the reins to the bit in the horse´s mouth and the horse is reinforced or rewarded for the correct response by softer contact or a release or pressure, depending on the style of riding. Studies have indicated that soft, consistent bit contact between the rider and horse causes the animal less stress than intermittent or unpredictable contact." - (en.wikipedia.org 17.09.2019)