Hyperbolic slit by mathematical methods proved a straight stick tilt rotation around the Z axis, which produces a hyperboloid, is perpendicular to the X, Y plane when the case is interesting tangent generated. Straight rods can pass through it subtly, because you can draw a circle is called a two-dimensional surface in the air straight line rotation, from the top of hyperbolic in the end portion in the curved edges to draw the line is called hyperbolic, Li board carved curve is hyperbolic, but also coincided with the straight rods of hyperbolic draw matches, so it can go through the hyperbolic slit on the plate.