Grzegorz Lesniewski / Brown Bear (Ursus arctos) sharpening its claws on a tree. Bieszczady National Park, the Carpathians, Poland, April.

Bryan and Cherry Alexander / Yupik Eskimo woman sharpening Ulu (traditional knife). New Chaplino, Chukotskiy Peninsula, Chukotka, Siberia, Russia, 2010

Anup Shah / Four African Lion cubs (Panthera leo) aged 3-6 months, sharpening their claws on tree trunk, Masai Mara National Reserve, Kenya. February

Petra Wegner / Sacred Cat of Burma / Birman, lilac-tabby-point coated, sharpening claws on log, in snow, with picket fence behind

Philippe Clement / European Brown bear (Ursus arctos) sharpening claws on tree in forest, Bavarian Forest NP, Germany, Captive

Eric Baccega / European brown bear {Ursus arctos} sharpening claws against tree trunk. Bayerisher wald NP, Germany. Captive

Pete Cairns / European Lynx (Lynx lynx) adult female sharpening claws on trunk in birch forest in winter, Bardu, Norway, captive

Pete Cairns / European Lynx (Lynx lynx) adult female at scratching post sharpening claws in winter birch forest. Bardu, Norway, captive

Rod Williams / Three Jersey bank voles {Clethrionomys glareolus caesarius} sharpening teeth on wood, captive, from Jersey, Channel Is, UK

Rod Williams / Oldfield mouse {Peromyscus polionotus} sharpening teeth on wood, captive, from North America

Shattil & Rozinski / Aspen tree with claw marks from Black bear {Ursus americanus} Colorado, USA

Anup Shah / Hadzabe bushman with traditional bow (string made from giraffe tendons) sharpening arrow. Lake Eyasi, Tanzania.