Closure Explanation

[bichonfrise74]

I got this code from this article perl.com.

sub make_counter {
    my $start = shift;
    return sub { $start++ }
}

my $from_ten = make_counter(10);
my $from_three = make_counter(3);

print $from_ten->() . "\n";
print $from_ten->() . "\n";
print $from_three->() . "\n";

I tried to read the article on the explanation of the code above but I could not figure out how it is able to 'retain/remember' the old values.
Can someone further dissect or rewrite this code to show what is exactly happening?