public class LayEggs {
  public static void main(String[] args) {
    Duck aDuck = new Duck("Donald", "Eider");
    Animal aPet = aDuck;                                               // Cast the Duck to Animal
//    aPet.layEgg();                                                   // This won't compile!
    ((Duck)aPet).layEgg();                                             // This works fine
   }
}