Dump the original and the copy using one call to Dumper, and the difference between a shallow and a deep copy will be obvious.

use Storable     qw( dclone );
use Data::Dumper qw( Dumper );

my %hash = (a=>{b=>{c=>1}});

my %shallow = %hash;
my %deep    = %{ dclone(\%hash) };

local $Data::Dumper::Indent = 1;

print("Shallow\n");
print("-------\n");
print(Dumper(\%hash, \%shallow));

print("\n\n");

print("Deep\n");
print("----\n");
print(Dumper(\%hash, \%deep));
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Shallow
-------
$VAR1 = {
  'a' => {
    'b' => {
      'c' => 1
    }
  }
};
$VAR2 = {
  'a' => $VAR1->{'a'}
};


Deep
----
$VAR1 = {
  'a' => {
    'b' => {
      'c' => 1
    }
  }
};
$VAR2 = {
  'a' => {
    'b' => {
      'c' => 1
    }
  }
};
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As you can see, the shallow copy clearly references back to the original, whereas the deep copy doesn't.