Monkeys are pretty smart. In this experiment, two monkeys were each given the task of giving the handler a rock, and in turn they received a treat. One monkey was given cucumber, which she happily ate, but the next monkey was given a grape. When the first monkey saw this, she happily gave handed a rock to the handler again, expecting to get a grape the next time around. When she was once again given a cucumber, she showed that she wasn’t happy about it.