You have:

 my %words = {};
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You want:

 my %words = ();
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Or better yet:

 my %words;
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Essentially in that first line, you're adding an entry to the hash where the key is a reference to an anonymous second hash, and the value is undefined. Because you can't use references as hash keys, the reference is stringified (which looks like a memory location).

In other words, my %words = {}; is basically a shorthand for:

 my %words;
 my $ref_to_anon_hash = {};
 $words{ $ref_to_anon_hash } = undef;
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