foreach my $key (keys %{$data->{blah}[$idx]{blih}}) {
  print "$key : $data->{blah}[$idx]{blih}{$key}\n";
}

##</code><code>##

while (my ($key, $value) = each %{$data->{blah}[$idx]{blih}}) {
  print "$key : $value\n";
}

##</code><code>##

foreach my $key (keys %{$data->{blah}[$idx]{blih}}) {
  my $value = $data->{blah}[$idx]{blih}{$key};
  ...
}