StaticMammal.pm (The equivalent of your A):

#!/usr/bin/perl -wT

package StaticMammal;

use strict;
use warnings;

sub new {
    my ($class) = @_;
    my $new_critter = bless {}, $class;
    return $new_critter;
}

sub walk {
    my ($self) = @_;
    print "A " . ref( $self ) . " walks " . $self->walks_how() . "\n";
    return;
}

sub talk {
    my ($self) = @_;
    print "A " . ref( $self ) . " says " . $self->talks_how() . "\n";
    return;
}

sub walks_how {
    return q(ponderously);
}

sub talks_how {
    return q(Grrr);
}


1;
__END__
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#!/usr/bin/perl -wT

package DynamicMammals;

use strict;
use warnings;

use lib '.';

my %style_of
    = (
       Cat => {
           talks => q(meow),
           walks => q(in beauty, like the night),
       },
       Dog => {
           talks => q(woof),
       },
       FrankenMammal => {
           ## empty hash
       },
       );

my $package_str = q();
foreach my $mammal (keys %style_of) {
    $package_str .= qq(
                       package Dynamic$mammal;
                       use base qw(StaticMammal);
                       );
    my $action_href = $style_of{ $mammal };
    foreach my $action (keys %$action_href) {
        $package_str
            .= sprintf q(
                         sub %s_how {
                             return q(%s);
                         }
                         ), $action, $action_href->{ $action};
    }
}

eval $package_str;
if (my $msg = $@) {
    die "Eval error: $msg\nwhile trying to eval:\n$package_str";
}


1;
__END__
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#!/usr/bin/perl -wT

use strict;
use warnings;

use lib '.';
use DynamicMammals;

my $felix = DynamicCat->new();
my $spot  = DynamicDog->new();
my $thing = DynamicFrankenMammal->new();

foreach my $critter ($felix, $spot, $thing) {
    $critter->walk();
    $critter->talk();
}

__END__
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