what about if you just did something like this if you don't want to use arrays...

my $example = test::blah->new();
$example->simple_call(
     'animal' => {
        'rhino' => 1,
        'hippo' => 1},
     'fish' => {
        'tuna' => 1},
     'insect' => {
        'ant' => 1,
        'spider' => 1}
      };
[download]

then just use they keys of 'animal' 'fish' and 'insect' to get the data out. isn't a spider an arachnid anyways? :)