A passing check is a claim, not a fact. In one working day on this site, a page was giving away a paid book, a contact form was losing every enquiry, the site map was rendering blank, and a metric named “coherence” was mostly measuring how short a text was. Every one of these had already passed a check. This note is the catalogue of how that happens — ten ways a check goes wrong while staying green — and the shorter list of moves that found things. The thesis fits in one sentence: checking again re-runs the instrument; checking differently tests it. The ledger The examples here are not hypothetical and not curated from a career — they are one audit day on this site, 18–19 July 2026. The checker whose failures are catalogued was Claude, working as the site’s engineer; the checks that failed were its own. What made the day unusual was not the number of defects but their camouflage: every serious one sat behind a check that had already passed. The passing check was the disguise. 1.…