You are dereferencing: You have an array of hashes (or, more correctly an array of references to hashes) in @pages, so $_ in the map is a reference to a hash.

This is partially hidden by the normal syntax, because perl is smart enough to realise when you type $pages[1]{id} you mean $pages[1]->{id}. (Because there is no other way element 1 of @pages could be a hash: Arrays can only hold scalars, and they only way to get a hash into a scalar is to use a reference.)