Animals use tools to get food, communicate with one another, defend themselves or even have a scratch. But in Chester Zoo, England, one monkey uses tools to give itself a pedicure.

Riccardo Pansini and Jan de Ruiter from Durham University watched a 18-year-old mandrill called JC clean his toenails out using small splinters. He made them himself, fashioning them from wood chips and twigs on the floor his enclosure, and honing them till they were small and sharp.

JC is the alpha male of the zoo’s six-strong group of mandrills. Over three months of observations, Pansini and de Ruiter saw JC give himself a pedicure seven times. On a couple of occasions, he ignored the wood altogether and just plucked out one of his own hairs to clean his nails with.

Many animals will use tools, but it’s not often that they modify those tools to make them more suitable for their needs. Chimps do it, as do New Caledonian crows. Among monkeys, biologists have documented a capuchin dressing her baby’s head wound with modified plants, spider monkeys making back-scratchers out of sticks, and Japanese macaques ...