use strict;
use warnings;

my ($mary, $lamb) = (bless({}, 'Girl'), bless({}, 'Lamb'));

push(@{$mary->{possessions}}, $lamb);
$lamb->{attributes} = { size => 'little', fleece => 'white as snow' };
$lamb->{location} = \$mary->{location};

# And to test...
$mary->{location} = 'town';
use Data::Dumper;
print Dumper $mary, $lamb;