The gag is a type of bit that uses leverage-cheeks (there is no curb chain, so no true leverage) to increase its severity. It works on the horse's lips and poll simultaneously. The pressure on the lips tends to make the horse raise its head, which is useful for a horse that tends to take a bit down and run off. However, a gag bit encourages a high, stiff neck. Gag bits are used mainly for horses that are strong pullers or for horses that need retraining. Gag bits are most commonly seen in polo, eventing (especially for cross-country), and show jumping. They are not permitted at any level of dressage, and are never seen worn by hunter seat horses.