cheaters

No I'm not going to talk about illegal drug use in racehorses - "cheaters" are blinkers with very small or narrow cups (people unfamiliar with racing sometimes call blinkers a "hood" or "blinders"). Cheaters can be used on a horse that you want to try without blinkers without declaring "blinkers off" when entering a race.  This way the trainer can get some idea if the blinkers can come off for good, and if the experiment doesn't work can still go back to regular blinkers for the horse's next race.