This is a riddle about everyday appliances. Described here is a woodworking tool called a wood plane. A wood plane is one kind of traditional tool used to create a level surface or object face. Wood planes are composed of three different parts: the planer, plane iron, and peg/driver. When this riddle asks, “what eats on its underside and casts things away on its back?” the answer is a traditional wood plane, which shaves a flat surface using a blade on its bottom and funnels shavings out of its back. As more modern tools are developed, fewer and fewer carpenters use this kind of traditional wood plane.