in reply to biased random number picking

So, essentially you want to sample w/o replacement. If you don't want to make a complete copy of your array (because it is very large or whatever), you can use the random_permuted_index() method from Math::Random. Another benefit to this module is that (as I understand it), the randomization is 'more random' than for rand; however, it may not be an issue in your case. Also, if you want to keep grabbing two at a time over and over, try splice regardless of how you do your sampling. (Splice is like shift/pop on 'roids.) Here is an example: 
#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;
use Math::Random;

my @array = qw( cat dog shark frog chimp seahorse );
my @permuted_index = random_permuted_index( scalar(@array) );

print "Here is your entire set:\n";
print Dumper @array;
print "Here is a random pick of two:\n";
print Dumper @array[ splice( @permuted_index, 0, 2 ) ];
print "And another two (unique from 1st two):\n";
print Dumper @array[ splice( @permuted_index, 0, 2 ) ];
print "And the final two:\n";
print Dumper @array[ splice( @permuted_index, 0, 2 ) ];

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Sample output:

Here is your entire set:
$VAR1 = 'cat';
$VAR2 = 'dog';
$VAR3 = 'shark';
$VAR4 = 'frog';
$VAR5 = 'chimp';
$VAR6 = 'seahorse';
Here is a random pick of two:
$VAR1 = 'dog';
$VAR2 = 'shark';
And another two (unique from 1st two):
$VAR1 = 'seahorse';
$VAR2 = 'frog';
And the final two:
$VAR1 = 'cat';
$VAR2 = 'chimp';

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