The bit is designed to cause discomfort, with the hope that the horse will avoid the discomfort and respond in a specific way - a response that will satisfy the rider. Sad, isn't it! Please watch!
There are two types of bits, a snaffle and a curb. The snaffle is the most common that consists of a mouth piece and rings on each side, and works on several parts of the mouth with direct pressure, without leverage. It acts on the tongue, bars, lips and the horse feels pressure from both the mouthpiece and rings, and the sides of the jawbone, depending of the design. The snaffle is not always jointed, does not have a shank and not always mild; although, milder than pressure with leverage. An ounce of pressure applied by the reins will apply an ounce of pressure on the mouth. Not so with a curb bit.
The curb bit is a type of bit that uses leverage (shanks) and is generally more severe than a snaffle. The curb works on the tongue, bars and the roof of the mouth. The shanks work on the poll, via the crown band, and the chin via the curb chain, causing poll and TMJ discomfort. The shank amplifies the reign pressure many times more than rings. Then longer the shank the more reign pressure! for every pound of pressure on the rein equals approximately four pounds of pressure on the horses mouth, tongue, bars, chin and poll. Heavy rein hands will eventually cause behavior problems due to pain and anticipated pain.