Music:Wolfgang Amadeus Mozart: Piano Concerto No.9 in E flat Major KV 271 - Andante
Animals understand fairness
Some amusing research on animals. If you train monkeys to give you a rock in exchange for food, they'll do it, even for a cucumber. However, if they see you giving another monkey better food for a rock, they'll get pissed at you, to the point of throwing away the food and not participating any more.
Dogs are less discriminating. So long as you feed them, they don't complain about the quality of their bribes. So if you teach them to shake, they'll do it for free. But, if they see another dog getting rewarded for shaking, they'll shake more slowly, and eventually stop shaking your hand, if you don't feed them, too.