use strict;
use warnings;

my $string = "God dog";

my $re =        qr/^
                  (.+)
                  (??{
                    (
                          length $^N > 1
                      and lc $^N eq reverse lc $^N
                    ) ? '' : '1\b2'
                  })
                $/ix;

print "$string is", ($string =~ $re) 
                  ? ""
                  : "n't", 
      " a palindrome.\n";