Effects The mouthpiece of the bit does not rest on the teeth of the horse, but rather rests on the gums or "bars" of the horse's mouth in an interdental space behind the front incisors and in front of the back molars. When a horse is said to "grab the bit in its teeth" they actually mean that the horse tenses its lips and mouth against the bit to avoid the rider's commands (although some horses may actually learn to get the bit between their molars). Depending on the style of bit, pressure can be brought to bear on the bars, tongue, and roof of the mouth, as well as the lips, chin groove and poll. Bits offer varying degrees of control and communication between rider and horse depending upon their design and on the skill of the rider. It is important that the style of bit is appropriate to the horse's needs and is fitted properly for it to function properly and be as comfortable as possible for the horse. Snaffle or direct pressure bits All bits work with either direct pressure or leverage. Bits that act with direct pressure on the tongue and lips are in the general category of snaffle bits. Snaffle bits most commonly have a single jointed mouthpiece and act with a nutcracker effect on the bars, tongue and occasionally roof of the mouth. However, any bit that operates only on direct pressure is a "snaffle" bit, regardless of mouthpiece. Curb or leverage bits Bits that have shanks coming off the bit mouthpiece to create leverage that applies pressure to the poll, chin groove and mouth of the horse are in the category of curb bits. Most curb bit mouthpieces are solid without joints, ranging from a straight bar with a slight arch, called a "mullen" mouthpiece, through a "ported" bit that is slightly arched in the middle to provide tongue relief, to the full spade bit of the Vaquero style of western riding which combines both a straight bar and a very high "spoon" or "spade" extension that contacts the roof of the mouth. The length of the shank determines the degree of leverage put on the horse's head and mouth. Again, a bit with shanks and leverage is always a "curb" type bit, even when it has a jointed mouthpiece more commonly seen on a snaffle (such bits are sometimes—incorrectly—called "cowboy snaffles"). All