Special literals taken literally

[xdg]

Sometimes, mistakes stare you in the face and you still miss them. This brief meditation is on the topic of special literals, one of which recently caused a frustrating bug for me. Realizing what had happened was a bracing reminder about when to use the cruciform operator.

For beginning to intermediate monks, ponder the following code snippet:

# In the file 'literal.pl'
package Illumination;
use strict;
use warnings;
use Data::Dumper;

my %hash;
$hash{__PACKAGE__}{__FILE__}{__LINE__} = "Mu Mu";

print Dumper \%hash;

What will it produce? Check your answer.