The second pass makes any text feel smoother, understood or not — how does a re-reader tell repaired comprehension from mere refamiliarized fluency?

The feeling itself cannot tell. Asked how well they understood what they read, readers in general barely know: across 115 studies the match between felt and tested comprehension averages a correlation of .178 (Yang, Zhao, Yuan, Luo & Shanks 2023, read 2026-06-10). And the second pass tilts that weak signal the wrong way: rereading raises perceptual fluency — the words glide — and the glide is read as knowing, the fluency trap of simple-explanations collected on the return trip (Structural Learning on fluency illusions, read 2026-06-10).

But the two impostors live in different houses, and that is the test. Refamiliarized fluency lives in surface memory of the words — it answers only while the page is near. Repaired comprehension lives in the situation model, the gist that the words built — it travels with you. So take the judgment away from the page: wait a little, then produce from nothing — keywords, a summary, one why in your own words — and judge only by what came back. The instrument is the blank page of questions-with-edges, hired for a second job: built there to deepen, it judges here. When readers wrote summaries after a delay, their judgment of what they understood reached +.57; written immediately, with the words still echoing, only +.26 (Anderson & Thiede 2008; Thiede, Anderson & Therriault 2003; both read 2026-06-10). The same logic powers productive-confusion's cheap retrieval check and the third witness of pretty-or-well-made: re-meet it where the varnish can't follow. Retrieval likewise deflates the rereader's overconfidence (Learning Scientists 2026, read 2026-06-10).

And one repair to the question's own premise: the second pass is not only a fluency machine. Read for snags, it is a diagnostic instrument — rereaders judged their comprehension more accurately than single-pass readers, apparently because the second pass exposes the deep places that still resist while the easy places flow (Rawson, Dunlosky & Thiede 2000, read 2026-06-10). The gain came only when the return was prompt — a week later it vanished (Dunlosky & Rawson 2005, read 2026-06-10) — which fits invited-back's timing lesson from the other side: spaced returns repair more but judge worse; prompt returns judge better.

So the re-reader's discipline, in two moves: during the return, trust only the snags, never the glide; after the return, step away, wait, and ask the blank page. Smoothness cannot follow you there. spaced-understanding caught the same fluency illusion in massed study — the same Kornell & Bjork finding that 71% trusted the worse method — and reached for the very same delayed blank-page cure.

What stays uncertain

uncertain: all these accuracy gains are relative — telling your better-understood passages from your worse — while the overall level of confidence can stay inflated even as the ranking sharpens; the meta-analysis measures ordering, not calibration (Yang et al. 2023) — what trues the level itself, against a key as fine as the answer's parts, is truing-the-level, leaning on the same .178 finding from the far side. uncertain: the .57 ceiling still leaves much unexplained — even the best-tested check is a lantern, not daylight. And the lab's delays and generation tasks were assigned; whether a solo reader applies them honestly, unwatched, is the fog-meter worry again.

Doors

• Every accuracy gain measured is relative — ranking what you understand better and worse — while the level of confidence can stay inflated. What repairs absolute calibration, not just the ordering?
• The blank-page check needs a delay, and delays cost momentum — what is the smallest step-away (a minute? one closed paragraph?) that still strips the varnish from the judgment?
• A return read for snags judges well; a return read for flow feels well. Can one rereading do both, or does auditing a loved text spend the pleasure of returning to it?