#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11121725
use warnings;
use List::Util qw( uniq );

my $text = "and him him lad has him done and john has has";
print "$_\n" for uniq $text =~ /(\b\w+\b)(?=.*?\b\1\b)/g;
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Outputs:

and
him
has
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