use strict;
use warnings;

my %HoA = (
    flintstones => [qw/fred barney george/],
    jetsons     => [qw/george fred elroy/],
    simpsons    => [qw/fred marge bart barney/]
);

my (%dupes, $k1, $k2, $i);

### Count instances of each word.
### I'm assuming, for the sake of argument, that there
### are no duplicates inside each array.
for $k1 (keys %HoA) {
    $dupes{$_}++ for @{$HoA{$k1}};
}

### For each duplicated word
for $k2 (sort keys %dupes) {
    next if $dupes{$k2} < 2;

    ### Output matches
    for $k1 (sort keys %HoA) {
        for ($i = 0; $i <= $#{$HoA{$k1}}; $i++) {
            print "\$HoA{'$k1'}[$i] = '$k2';\n"
                if $HoA{$k1}[$i] eq $k2;
        }
    }
    print "\n";
}