#!/usr/bin/perl -w
use warnings;
use strict;

my @animals = ("cat", "dog", "fish", "horse", "pig");

my %count;

while (<DATA>) {
        my ($x,$y) = split /\s/;
        ($x,$y) = ($y,$x) if ($x gt $y);
        $count{$x}{$y}++;
}

for my $x (sort keys %count) {
        for my $y (sort keys %{$count{$x}}) {
                print $count{$x}{$y}," people have both a ",
                        $x, " and a ", $y, "\n";
        }
}

__DATA__
cat dog
cat fish
pig dog
horse fish
pig fish
dog fish
fish cat