#!/usr/bin/perl -w
use strict;
use Data::Dumper;

my @x= qw(1 2 3 4);
my @y= qw(7 8 9 10 11 12 13 14);

my $num = $y[@x];  # @x evaluates here to the number "4"!!!
                   # the number of elements in @x
                   # As said before this is a VERY unusual 
                   # formulation!!!
                   # It looks weird because it is weird.
                   # As mentioned above more normal would be
                   # $y[@x-1] or $y[$#x]
                   # I'm not saying that $y[@x] cannot have a defined,
                   # value but just that it is "strange" absent other
                   # context and would be worthy of a comment in the
                   # code.

print "The number in y is: $num\n";  #the 5th thing in @y!! WHOA!

#print $x[@y]; # ERROR: Use of uninitialized value in print
               # this is because: $x[8] is undefined!

# However consider this:
# here [@x] means something completely different

push @y, [@x]; # this means: assign new memory,
               # copy @x into that new memory ,
               # push a reference to that memory 
               # onto @y
               
print Dumper \@y;

__END__

The number in y is: 11  ### the 5th thing in @y
$VAR1 = [
          '7',
          '8',
          '9',
          '10',
          '11',
          '12',
          '13',
          '14',
          [
            '1',
            '2',
            '3',
            '4'
          ]
        ];