{ package Animal;
  sub named {
    my $class = shift;
    my $name = shift;
    bless \$name, $class;
  }
  sub name {
    my $either = shift;
    ref $either
      ? $$either # it's an instance, return name
      : "an unnamed $either"; # it's a class, return generic
  }
  sub speak {
    my $either = shift;
    print $either->name, " goes ", $either->sound, "\n";
  }
  sub eat {
    my $either = shift;
    my $food = shift;
    print $either->name, " eats $food.\n";
  }
}
{ package Horse;
  @ISA = qw(Animal);
  sub sound { "neigh" }
}
{ package Sheep;
  @ISA = qw(Animal);
  sub sound { "baaaah" }
}

Now try it out:

my $tv_horse = Horse->named("Mr. Ed");
$tv_horse->eat("hay");
Sheep->eat("grass");

It prints:

Mr. Ed eats hay.
an unnamed Sheep eats grass.

Animal::eat($tv_horse, "hay");