It’s a simple rule: If you want a job done right, choose the right tool for the job.

Carpenters know it well; so do plumbers, masons and car mechanics, to name a few trades.

And capuchin monkeys, apparently.

Researchers have found that bearded capuchin monkeys in the wild will select the most effective stone for use in cracking nuts, rejecting those that are too light or crumbly. They make the right choice by looking at the stones but also by lifting or tapping them if necessary.

Image A capuchin monkey after choosing the heavier stone for his work.

Elisabetta Visalberghi of the Institute of Cognitive Sciences and Technologies of the National Research Council in Rome and colleagues studied a group of the monkeys in Brazil that was discovered in 2003 to use stones as hammers to open palm nuts, which are difficult to crack. Until then there had been only a few anecdotal reports of tool use by these primates.