The points on the horse's head that can be affected by a bit or some type of headgear include the tongue, bars, cheeks, lips, palate, nose, curb area and poll. Some pieces of headgear may be able to affect nearly all of these points while some may only affect two or three of these points. Snaffle bits are considered direct pull bits because when the rider pulls on the reins, that pressure is transmitted directly to the horse's mouth. It is a common misconception in the industry that a snaffle bit is one that has a broken mouthpiece; that is, the mouthpiece is comprised of at least two pieces. This is wrong, even though many catalogs, books and "experts" propagate it. A snaffle bit may have a solid mouthpiece, a two-piece mouthpiece, a three-piece mouthpiece or multiple links such as a chain. The mouthpiece may or may not have a port, rings, keys, dogbone, etc. The key to identifying a snaffle is that it is a bit that operates off of direct pull; there is no leverage involved. The reins on a snaffle bit attach directly to the mouthpiece, not to a shank. A curb bit, on the other hand, involves leverage, which means the reins are attached to a shank of some design. A curb strap of some type is used under the horse's chin. When the rider pulls back on the reins, pressure is applied not only to the horse's mouth and chin but also to the horse's poll; this is the leverage effect. It requires that the reins not attach directly to the mouthpiece, but instead to some type of shank on the bit. The reins attach to the bottom part of the shank and the cheek pieces of the bridle attach to the upper part of the shank. As the rider pulls back on the reins, the top part of the shank moves forward as far as the curb strap will allow. This creates the leverage. The tighter the curb strap, the less pressure applied to the poll. The looser the curb strap, the more pressure can be applied to the poll as the top of the shank can move farther forward. Even if a curb is not used, there is still leverage on the horse's poll due to the fact that the reins are not attached directly to the bit but instead to a shank that rotates forward when pressure is applied to the reins. Poll pressure can be a very effective tool in eliciting certain responses from the horse. Horses are naturally inclined to move away from poll pressure and therefore will often lower their heads and flex at the poll to escape this pressure. This is a desired response used to achieve greater performance in many disciplines. However, to perform correctly in a curb bit, the horse must have already learned how to be guided willingly and submit to bit pressure. Too much poll pressure too early in a horse's training will often cause the horse to either fight or evade the bit.