Monkey gets upset about receiving unequal pay (Video)

Dutch primatologist and ethologist Frans de Waal shows a video of two Capuchin monkeys in side-by-side cages. Each monkey is given the same task to complete: handing the experimenter a rock. Their "pay" is a slice of cucumber. But when the experimenter starts paying one of the monkeys in grapes (which the monkeys like better than cucumbers), the monkey who was being paid in cucumbers protests.
(Via 22 Words)