Capuchin monkey
When they see macaws eating palm nuts, cracking them open with their beaks, capuchins select a  few of the ripest fruits. They nip off the tip of the fruit and drink down the juice, then seemingly discard the rest of the fruit with the nut inside. When these discarded fruits are hardened and brittle, the capuchins gather them up. Then they take them to a large flat boulder where they already have a few stones from a river. They use these stones to crack open the fruit to get to the nut inside. Young capuchins watch this process to learn from the more experienced adults. It may take a capuchin up to eight years to master this skill.