$stuff = [ 'cat', 'dog', 'pig', 'cow' ];

my %stuff map { $_ => 1 } @$stuff;
my @elements = keys $stuff;

for ($elements[int rand scalar @elements]) {
  $stuff{$_} = 0;
  @elements = grep $_, keys %stuff;

  # your code here, $_ being either a cat, a dog, etc.

}

for (keys %stuff) { $stuff{$_} = 1 }