Abe and Bev both look in a plane mirror directly in front of Abe (left). Abe can see himself while Bev cannot see herself - but can Abe see Bev, and can Bev see Abe? To find the answer we construct their virtual locations "through" the mirror, the same distance behind as Abe and Bev are in front (right). If straight-line connections intersect the mirror, as at point C, then each sees the other. The mouse, for example, cannot see or be seen by either Abe or Bev.