Here is the splice version. Make sure you understand what's going on before you submit to whomever... (there is a twist...)

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

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

my @mixed = interleave_words( scalar(@first), @first, @second );
print "Result: @mixed\n";

sub interleave_words
{
  my $count = shift;
  my @results = splice @_, $count;       
  foreach my $index ( 0 .. $count-1 )
  {
    splice @results, 2*$index, 0, shift; 
  }
  return @results;
}
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