A round roof of a garage changes its appearance to a corrugated roof when it is reflected in a mirror. The actual shape is neither round nor corrugated. This illusory solid was discovered by combining two observations. One is a mathematical observation that a single image does not covey depth information, and the other is a psychological observation that the human brains like right angles in interpreting an image. Indeed we are apt to interpret the edge curve of the roof as an intersection of a roof with a plane perpendicular to the axis of the roof.