Considered separately, each rein can produce four important and distinct effects:
(1 ) Front to rear effect.—The rider pulls on the two reins alike, without pressing them on the neck and without opening the wrists. If the horse is moving, he will decrease the gait or halt; if the horse is halted, he will move backward.
(2) Opening effect.—The rider opens the right rein by carrying the wrist to the front and right. The horse's head will be drawn to the right and he will move in that direction. This is the direct rein.
(3) Bearing or pushing effect.—By pressing the left rein against the neck, the mass (forehand) is pushed to the right and the horse faces in that direction—this is the indirect rein, sometimes called the supporting rein.
(4) Opposing effect.—The rider opens the right rein lightly and then pulls either in the direction of the right haunch or in the direction of the left haunch. He is then said to set the shoulders in opposition to the haunches. The rein of opposition comes to the aid of the leg on the same side when the latter's action is insufficient or incomplete.
- In the United States Cavalry Drill Regulations a horse is described as "rein wise when he obeys the lightest pressure of the rein on either side of the neck, the bit not being disturbed from its normal position." It is to be noted that the horse has learned to obey this pressure (third effect) through its association with the opening of the leading rein, as prescribed in paragraph 216, Drill Regulations (second effect). When the rider uses the direct or leading rein, there must be sufficient tension on the other rein to prevent the bit from "being disturbed from its normal position," and the other rein (la rêne opposée) is also pressed against the neck to support the action of the direct rein. In general, there must be combined action of the reins just as there must be combined action of the legs (see "Unison of the legs, in the next question), and this fact should be kept in view in the discussion of the distinct effects produced by the reins. The text reads: "Considered separately, each rein, etc.," which might be erroneously construed as "Each rein, acting alone, etc."-The Board.