A single comma can completely reverse a sentence's meaning

Truss's title joke — a panda that "eats, shoots and leaves" versus one that simply "eats shoots and leaves" — is deployed as the book's central proof that punctuation isn't a cosmetic detail but a functional carrier of meaning capable of turning a description of bamboo-eating into an account of an armed robbery.

She uses this and similar examples to argue against the common dismissal of punctuation complaints as pedantry, insisting instead that the whole point of punctuation is disambiguation: without it, written language loses precision that spoken language recovers through tone, pause, and emphasis, meaning careless punctuation creates exactly the kind of confusion that careful spoken communication naturally avoids.

Her broader claim is that every punctuation mark exists because plain sequences of words are frequently genuinely ambiguous, and that the marks we now take for granted were solutions to real, recurring comprehension problems rather than arbitrary decorative conventions imposed for their own sake.

Takeaway: before dismissing a punctuation error as trivial, check whether it actually changed what the sentence means.