What is a dumb jockey?

A dumb jockey is a harness for training horses that supposedly has a similar effect to a rider on the horse's back, including weight and resistance to the mouth. Dumb jockeys were traditionally used for the first stages of breaking, particularly in Europe, so that a real person would not be hurt if they freak out. Some variants hold the reins very tightly - and these variants are now seldom used as they resist without any give and many think they hurt the horse's mouth. Some argue that they should not be used at all.