Question: I'm sending a subroutine a hash, and fetching it with `my($arg_ref) = @_;`

But what exactly is `%$arg_ref`? Is `%$` dereferencing the hash?

Answer: 
Instead of dereferencing the entire hash like that, you can grab individual items with 

```
$arg_ref->{key}

```
A good brief introduction to references (creating them and using them) in Perl is `perldoc perfeftut`. You can also [read it online](http://perldoc.perl.org/perlreftut.html) (or get it as a pdf). (It talks more about references in complex data structures than in terms of passing in and out of subroutines, but the syntax is the same.)