Hikers using the trails that wind through the dense forest that surrounds the main dish at Arecibo sometimes take a wrong turn and find themselves on the path that ends "inside" the dish, instead of "under" the dish.  The radio signals that reflect off the dish can cause disorientation which often makes the hikers raise their arms and spin around deliriously, thereby deflecting  the signals and causing them to be read as false gaussians in the shape depicted on this example.