use warnings;
use strict;
use Data::Dumper;
use Tie::Hash;

package FlatHash;
use Data::Dumper;
our @ISA = qw(Tie::ExtraHash);

sub STORE {
    my $me    = $_[0];
    my $key   = $_[1];
    my $value = $_[2];
    $key = lc $key;
    $_[0][0]{$key} = $value;

    if(ref $value eq "HASH") {
        warn Dumper($value);
    }
    else {
        print "This isn't a hash\n";
    }
}

package main;

tie my %flat, "FlatHash";
$flat{Monkey}{habits} = "Eating";
$flat{monkey}{habits} = "Scratching";

warn Dumper(\%flat);