PRIMATES apart, few mammals employ tools. Sea otters use rocks to smash clams open, dolphins wrap sponges around their noses to protect themselves while they forage on the seabed, elephants swat insects with branches and humpback whales exhale curtains of bubbles to trap schools of fish. Until now, these four examples had been thought the extent of the non-primate mammalian tool-users club. But a study just published in Animal Cognition, by Volker Deecke of the University of St Andrews, in Britain, has added a fifth and rather surprising one. That epitome of rugged wildness, the grizzly bear, seems to be the only species other than humans to have invented the comb.

Dr Deecke made this discovery while studying grizzly-bear behaviour from a small boat in Glacier Bay National Park, Alaska, on July 22nd 2010. After a period of play-fighting with another bear and a short bout of feeding on a beached whale carcass, a bear of between three and five years of age, sex unknown, waded into the shallows of the bay. Once there, it picked up a fist-sized rock and carefully rotated it for about a minute before dropping it back into the water. Moments later, it picked up another, of similar size, and again rotated it. This time, rather than discarding the stone, it held it against its muzzle and started to rub. Using its left paw to press the rock against its skin and its right paw to support the rock's weight, the bear rubbed away at its muzzle and face for roughly a minute before dropping the stone back into the water. Then it grabbed a third stone of the same size, rotated it and rubbed its face, muzzle and neck for a further two minutes before discarding it. This done, it spent two minutes grooming its right paw with its teeth before returning to the whale carcass.

Dr Deecke found, upon close examination of his photographs, that all three rocks were encrusted with barnacles and he reckons these were acting as the functional equivalent of the teeth of a comb. He thinks the bear was probably using its makeshift combs for comfort, rather than vanity. But crucially for the concept of tool-use, the animal's rejection of the first rock it picked up shows a discriminating understanding of what was required to get the right amount of scratching from a comb; which rock, in other words, was the tool for the job.

An important question from a biological point of view is whether this animal's behaviour is unique. Other tool-using mammals are social species. That means one individual's chance invention is easily copied by others of its group, resulting in a primitive culture. Grizzly bears have not been considered particularly sociable in the past, but if others in Glacier Bay are seen combing themselves in this way that view might have to change. It might, though, be that Dr Deecke's preening animal is unique. That would suggest it came up with the idea of using rocks as combs by itself, rather than copying someone else—truly smarter than the average bear.