Depth-3 center-embedded sentences such as 'Vehicles that engineers who car companies trust build crash every day' are semantically plausible yet practically incomprehensible

The claim that English is not accepted by any finite-state automaton can only be supported by showing that every grammar for English has center- embedding to an unbounded depth (see Levelt 2008: 20–23 for an exposition and proof of the relevant theorem, originally from Chomsky 1959). But even depth-3 center-embedding of clauses (a clause interrupting a clause that itself interrupts a clause) is in practice extraordinarily hard to process. Hardly anyone can readily understand even semantically pl