Brummagem England was toppling already and her downfall would be Ireland, her Achilles heel, which he explained to them about the vulnerable point of Achilles, the Greek hero, a point his auditors at once seized as he completely gripped their attention by showing the tendon referred to on his boot.
There are no more uses of "tendon" in the book.
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She ruptured her left Achilles’ tendon.
Peony’s fingers twitched when Cinder hit a tendon, making her jump.