Chairs are the solid shadows of humanity and indeed of all animal life. It is not just that they have legs. They have feet, or at least claws. At the Brooklyn Museum's recent Converging Cultures exhibit I saw a massive Peruvian eighteenth-century ecclesiastical armchair with spooky toe joints. And the jargon of furniture continues the metaphor.
Chairs have knuckles.
They have knees. They have elbows. Chairs have seats and backs, often reverse contours of our own. They have arms, often the size of ours. The protruding corners of Chippendale chairs are called ears.