This is why we use strict! The extra arrow is unneeded, as you're working on the actual hash, not a reference to the hash. This is a compiler error with use strict though, so it's not something you would generally be bitten with when writing real code, just internet comments. :)

Whoops, good catch! I had references on the brain. For completeness, that makes it either

    $nested{$x}{$y}{$z}

or after initializing with curly brackets rather than parentheses to construct a new reference to an anonymous hash

    $nested = { … };

and then use the arrow to dereference as in the grandparent.

I think the point is not that Perl's rules don't make sense -- it's that they're much less obvious than those in many competing languages. In Python, lists are `l = [1, 2, 3]` and dicts are `d = {"key": val}`. Both structures can be nested without any change to the semantics.