use strict;
my $hash={};
$hash->{countries}->{USA}->{animals}->{fox}=1560;
$hash->{countries}->{Italy}={};
while ( my ($country, $country_ref) = each %{$hash->{countries}} ) {
 print "$country\n";
 print $country_ref->{animals}->{fox}."\n" 
    if exists $country_ref->{animals}->{fox};
};

##</code><code>##

$hash->{countries}->{USA}->{animals}->{fox}=1560;