{ package Animal;
  sub sound { "WOOOAAARRRR" }
  sub speak {
    my $class = shift;
    print "a $class goes ", $class->sound, "!\n";
  }
}

{ package Horse; 
  @Horse::ISA = qw(Animal);
  sub sound { "neigh" }
  sub p1 { print "p1: ". shift() ."\n"; }
}

Horse->speak();         # ok, works as expected

Horse::p1("Horse");     # ok, prints "Horse"

Horse::speak("Horse");  # Message:
                        # "Undefined subroutine &Horse::speak called..."
                        # So, the inheritance mechanism does not work for this?