In different breeds of dog certain steps of these five have been amplified or reduced by human-controlled selective breeding for various purposes. The "search" aspect of the prey drive, for example, is most valuable in detection dogs such as bloodhounds and beagles. The "eye-stalk" is a strong component of the behaviors used by herding dogs. The "chase" is seen most clearly in racing dogs such as Greyhounds and Lurchers, while the "grab-bite" and "kill-bite" are valuable in the training of terriers.