About namespaces and inheritance:

Namespaces, like "Animal::Dog", are just names, as was written before. Inheritance is defined differently, but it is good habit to create namespaces related with inheritance, for instance:

package Animal; #parent class, in file lib/Animal.pm 
sub new {
  return bless {}, shift;
}
sub sound {
  die "cannot call this method on class '".ref(shift)."'";
}
sub output_sound {
  my ($self, $what) = @_;
  print $what."\n";
}
1;

package Animal::Dog; #desc. of Animal, lib/Animal/Dog.pm
use base 'Animal';
sub sound {
  my ($self) = @_;
  $self->output_sound("haf");
}
1;

package Animal::Dog::Sheepdog; #desc. of Dog
                               #lib/Animal/Dog/Sheepdog.pm
use base 'Animal::Dog';
sub guard {
  my ($self, $flock) = @_;
  #do something
}
1;

package Animal::Pig; #other descendant
use base 'Animal';
sub sound {
  my ($self) = @_;
  $self->output_sound("khro");
}
1;
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Now you can create some instance of animal :>) by this way:

use Animal::Dog::Sheepdog;
my $helper = Animal::Dog::Sheepdog->new();

#Once you have an instance, you can call it's methods by this way:

$helper->sound;
[download]

Do not hesitate to ask some questions, I had been confused in the same manner. Just note: that code is not tested, it really should have strictings in every module...