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


my @first  = qw(Can unlock secret);
my @second = qw(you the code?);
my @interleave;

push @interleave, grep {$_} (shift @first), shift @second
    while @first || @second;

print "@interleave";

##</code><code>##

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

my @first  = qw(Can unlock secret);
my @second = qw(you the code?);

splice @first, @second, 0, pop @second while @second;

print "@first";

##</code><code>##

...
splice @first, $_, 0, $second[$_ - 1] for reverse 1 .. @second;

print "@first";

##</code><code>##

my @new;

splice @new, 0, 0, $first[$_], $second[$_] for reverse 0 .. $#second;
print "@new";

##</code><code>##

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


my @first = qw(Can unlock secret);
my @second = qw(you the code?);

dumpArrays('start', \@first, \@second);

splice(@first, 1, 0, @second[0,-2]);
dumpArrays('first', \@first, \@second);

my @newArray = @first;

splice(@newArray, 5,0,@second[0,2]);
dumpArrays('na', \@first, \@second, \@newArray);

my @newArray1 = @newArray;

splice(@newArray1, 2,1);
dumpArrays('na1', \@first, \@second, \@newArray1);

my @newArray2 = @newArray1;

splice(@newArray2, 4,1);
dumpArrays('na2', \@first, \@second, \@newArray2);

my @newArray3 = @newArray2;

splice(@newArray3,3,0, @second[1,1]);
dumpArrays('na3', \@first, \@second, \@newArray3);


sub dumpArrays {
    my ($msg, @arrays) = @_;

    printf "%-10s %s\n", $msg, join '|', map {"@$_"} @arrays;
}

##</code><code>##

start      Can unlock secret|you the code?
first      Can you the unlock secret|you the code?
na         Can you the unlock secret|you the code?|Can you the unlock secret you code?
na1        Can you the unlock secret|you the code?|Can you unlock secret you code?
na2        Can you the unlock secret|you the code?|Can you unlock secret code?
na3        Can you the unlock secret|you the code?|Can you unlock the the secret code?