"Penguins" joke

A Mexican newspaper reports that bored Royal Air Force pilots stationed
on the Falkland Islands have devised what they consider a marvelous new
game. Noting that the local penguins are fascinated by airplanes, the
pilots search out a beach where the birds are gathered and fly slowly
along it at the water edge. Perhaps ten thousand penguins turn their
heads in unison watching the planes go by, and when the pilots turn
around and fly back, the birds turn their heads in the opposite
direction, like spectators at a slow-motion tennis match. Then, the
paper reports, "The pilots fly out to sea and directly to the penguin
colony and overfly it. Heads go up, up, up, and ten thousand penguins
fall over gently onto their backs.