this was freaking weird.. sorry at least for me- maybe it's my terrible hangover. but.. here goes..

#!/usr/bin/perl

use strict;

my @a1=qw(yo and this too too too a b c d d d d d);

my @a2=qw(yo and too too x f 3 d d moon);


my %a1=();

my %a2=();

for (@a1){
    $a1{$_}++;
    #$found{$_}++;
}

for (@a2){
    $a2{$_}++;
    #$found{$_}++;
}


for (keys %a1){
    $a2{$_} or delete $a1{$_};
}

for (keys %a2){
    $a1{$_} or delete $a2{$_};
}

# now a1 and a2 both contain the same keys, but possibly diff values

my %highest=();

for (keys %a1){ # or a2, same thing
    if ($a1{$_} > $a2{$_} ){
        $highest{$_}=$a1{$_};
    } 
    else {
        $highest{$_}=$a2{$_}; # also if they are the same, non higher 
+then the other
    }
}

for (keys %highest){
    print "$_:$highest{$_}\n";
}
[download]

output is:

yo:1
d:5
and:1
too:3

hope that helps or amuses