In file Animals.pm, I have

package Cow;
sub Cow::speak {
    my $class = shift;
    print "$class Cow goes moooo!\n";
}

package Horse;
sub Horse::speak {
    my $class = shift;
    print "$class Horse goes neigh!\n";
}

package Sheep;
sub Sheep::speak {
    my $class = shift;
    print "$class Sheep goes baaaah!\n";
}

1;