As the previous poster stated, you are not calling open directly. You are calling the method $r->open(). A method is going to expect that you are passing an array of values.

Unqouted words have different means with different context,

my %hash = ( red => 'car' );  # Hash context
[download]

last STATEMENT;               # label context
[download]

open FILE, "my_file.txt";     # file handle context
[download]

$r->open( ARGS );  # looking for an array, and the interpreter is thin
+king,
                   # it cannot be a label or file handle and it is not
+ a hash, WTF?
[download]

I hope that helps some. Context of certain syntax can be confusing if you had not been doing it for a while, a loooong while! :) Note: This is within the context of 'use strict'.