Here is an approach that should work no matter how complicated your data structure becomes (provided the data you want remains in the form humps => d):

#! perl
use strict;
use warnings;
use Data::Dumper;

my $animals = {
                 gnu       => {
                                 humps      =>  0,
                                 mascot_for => 'emacs',
                              },
                 dromedary => {
                                 humps      =>  1,
                                 mascot_for => 'perl',
                              },
                 camel     => {
                                 humps      =>  2,
                                 mascot_for => 'perl',
                              },
              };

my $flat = Dumper($animals);
print "$1\n" while $flat =~ / 'humps' \s+ => \s+ (\d+) /gx;
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Output:

2
0
1
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TMTOWTDI.