Rearing can be caused by fear; a horse that sees something alarming in front of it may stop and, if asked to continue forward, may rear rather than move ahead. Another fear response may come from poor riding. A rider that is particularly hard on a horse's mouth with the reins and bit may provoke a horse to rear from the pain the horse feels in its mouth. A horse may rear out of confusion because it does not understand what the rider's commands, or riding aids mean, or because the rider is giving harsh or conflicting commands. If a rider both holds onto the horse's mouth at the same time they push the horse strongly with their legs, essentially using the "gas and the brake" at the same time, they can also provoke rearing.