The mouthpiece is the part of a horse's bit that goes into the mouth of a horse, resting on the bars of the mouth in the sensitive interdental space where there are no teeth. The mouthpiece is possibly the most important determinant in the severity and action of the bit. Some mouthpieces are not allowed in dressage competition. The other parts of the bit are the bit rings on a snaffle bit, and the shanks on a curb bit. These pieces do not go inside the mouth, but rather are the parts of a bit that are outside the mouth, where the bridle and reins attach.