foreach my $i (1..$cards) {
    my %seen;
       .
       .
       .
    for my $x (1..4) {
        for my $y (1..4) {
            my $word;
            while (1) {
                my $index = rand(@words);
                $word = $words[$index];
                if (!$seen{$word}) {
                    $seen{$word}++;
                    last;
                }
            }
              .
              .
              .