A slice of an empty list is still an empty list. Thus:
    @a = ()[1,0];           # @a has no elements
    @b = (@a)[0,1];         # @b has no elements

But:
    @a = (1)[1,0];          # @a has two elements
    @b = (1,undef)[1,0,2];  # @b has three elements

More generally, a slice yields the empty list if it indexes only beyond the end of a list:
    @a = (1)[  1,2];        # @a has no elements
    @b = (1)[0,1,2];        # @b has three elements

##</code><code>##

use strict;
use warnings;
use 5.014;  
use Data::Dumper;

my %hash = ('hello', 1, 'goodbye', 2, 'world', 3, 'mars', 4);
@hash{'goodbye', 'world'} = ();

say Dumper(\%hash);

--output:--
$VAR1 = {
          'mars' => 4,
          'hello' => 1,
          'world' => undef,
          'goodbye' => undef
        };

##</code><code>##

$VAR1 = {
          'mars' => 4,
          'hello' => 1,
        };

##</code><code>##


my @arr = (10, 20, 30, 40);
@arr[1, 2] = ();

say Dumper(\@arr);

--output:--
$VAR1 = [
          10,
          undef,
          undef,
          40
        ];