This riddle asks for an object which looks like a magpie entering a hole, leaving nothing exposed but its tail feathers. The image evoked is of a round hole with tail feathers jutting outward and down.  The shape visualized here is similar to a blinking eye—round yet shut, the eyeball obscured, with the eyelashes sticking out at the bottom. The magpie’s coloration, being black and white, is also reminiscent of a human eye.  And, even in hiding, covered by darkness, magpies maintain their connection to a closed human eye.