shanked bits require the use of a curb chain or curb strap for proper action and safe use. Combination designs Some bits combine both direct pressure and leverage, the most common examples being the Pelham bit, which has shanks and rings allowing both direct and leverage pressure on a single bit and is ridden with four reins; the Kimblewick or Kimberwicke, a hybrid bit that uses minimal leverage on a modified snaffle-type ring combined with a mouthpiece that is usually seen more often on curb bits, ridden with two reins; and the double bridle, which places a curb and a snaffle bit simultaneously in the horse's mouth so that each may act independently of the other, ridden with four reins. Another bit that combines direct pressure and leverage in a unique manner is the Gag bit, a bit derived from the snaffle that, instead of having a rein attached to the mouthpiece, runs the rein through a set of rings that attach directly to the headstall, creating extra pressure on the lips and poll when applied. Usually used for correction of specific problems, the gag bit is generally illegal in the show ring and racecourse. Idiomatic usage Bits and the behavior of horses while wearing bits have made their way into popular culture outside of the horse world. Took the bit in his teeth, a phrase that describes a horse that sets its jaw against the bit and cannot be controlled (rarely does the horse actually grab the bit with its molars), is used today to refer to a person who either is taking control of a situation or who is uncontrollable and casts off restraint Champing at the bit, or chafing at the bit, meaning to show impatience or burst with energy, refers to a tendency of some horses, when impatient or nervous, and especially if being held back by their riders, to chew on the bit, often salivating excessively. This behavior is sometimes accompanied by head-tossing or pawing at the ground. Because people often saw this behavior exhibited by horses lined up for a horse race before the invention of the starting gate, the term has come to describe a person who is eager to get started or to do something. Some impatient horses will rear when held back, so the related phrase "raring to go" also is derived from observations of equine behavior. See also Bit guard