There are many different types of bits, including snaffles, pelhams, and curb bits. They all work a little differently. Some bits are "softer" than others, meaning that a pull on it is gentler to the horse than a "harsh" bit. For example, bits with a smooth mouthpiece are soften than those with a twisted mouthpiece. Bits are not cruel when used correctly, but a rider that pulls too hard can hurt a horse's mouth, especially if they use a harsh bit. If a rider is inexperienced, they should ride with a softer bit so when they make mistakes they do not hurt the horse. Experienced riders who can follow the horse's mouth as the horse moves and give very slight cues can use bits that are harsher. They have the skill to use the bits for very fine control over the horse, without hurting it. 