file of choice

When I first saw this squirrel chewing on the metal fence, I thought it might be deficient in some mineral found in the paint or the metal. Then when I saw the little teeth marks left on the edge of the fence between the back paws and the front, I realized it was probably sharpening its teeth. So I Googled it, and sure enough, squirrels' teeth never stop growing so they need to file them down, as well as keep them sharp.