eval { print speak('sheep'), "\n"; };
print $@ if $@;

my %says = (
    sheep  => 'baa',
    monkey => 'foo',
);

eval { print speak('monkey'), "\n"; };
print $@ if $@;

sub speak {
    my $animal = shift;
    die unless defined $says{$animal};
    return $says{$animal};
}
__END__
Died at Perl-1.pl line 21.
foo

##</code><code>##

use 5.010_000;

eval { say speak('sheep'); };
print $@ if $@;

eval { say speak('monkey'); };
print $@ if $@;

sub speak {
    my $animal = shift;
    state $says = {
        sheep  => 'baa',
        monkey => 'foo',
    };
    die unless defined $says->{$animal};
    return $says->{$animal};
}
__END__
baa
foo

##</code><code>##

BEGIN {
    my %says = (
        sheep  => 'baa',
        monkey => 'foo',
    );

    sub speak {
        my $animal = shift;
        die unless defined $says{$animal};
        return $says{$animal};
    }
}

##</code><code>##

{
    my $says;

    sub speak {
        my $animal = shift;
        $says |= initialize_says();
        die unless defined $says->{$animal};
        return $says->{$animal};
    }
}

##</code><code>##

sub speak {
    my $animal = shift;
    state $says = initialize_says();
    die unless defined $says->{$animal};
    return $says->{$animal};
}