sub feedDucks
{
  while (my $object = shift)
  {
    if ( $object->can('walk') and $object->can('quack') 
     and $object->can('swim') and $object->can('feed') )
    {
      $object->feed('breadcrumbs');
    }else{
      warn "Insufficient mana to polymorph $object!";
    }
  }
}