From The Economist of July 27th. Yes, it’s grammatical, but it’s fiercely hard to parse — you might feel the need to get out pencil and paper to graph the thing — and it’s also a big show-stopper flourish: stop reading the news to admire how clever we are!
In this case, the magazine has committed a nested clausal comparative (NCC), somewhat reminiscent of nested relative clauses (also known in the syntactic literature as self-embedded relative clauses) like those in the NP with head the rat modified by the relative clause that the cat that the dog worried ate:
[ the rat ]-i
… [ that [ the cat ]-j [ that [ the dog ] worried ___-j ] ate ___-i ]
(where an underline indicates a missing (“extracted”) constituent, and the indices mark coreferential constituents). Both nested relatives and NCCs require the hearer to interrupt the processing of one clause to process another clause of similar form.
