Fable
The examiner who guessed who had attended school
In the city there was a private school that trained an answering puppet, and the essays students submitted were all used as demonstrations. The more the puppet answered like a student, the more pleased the teacher was. One day an out-of-town examiner brought an old essay and questioned the puppet. The puppet was unusually confident about this essay and could even add several details near the original sentences.
The examiner did not steal the account books, but inferred that this essay had been through a private school training workbook. If the essay content involved illness, complaints or trade secrets, the trouble would be considerable.
The teacher first cut the students' names off their essays. But the puppet remembered text patterns, not just signatures. The school began controlling training materials: deduplicating, limiting sensitive samples, reducing overfitting, and comparing the puppet's familiarity with essays inside and outside the practice set.
The external Q&A interface was also changed. The puppet no longer returns overly detailed confidence scores, abnormal repeated questions are rate-limited, and high-risk queries enter audit. When an examiner probes with an old essay again, the puppet gives a robust but not overconfident answer, and cannot easily reveal whether this essay has been seen.
The examiner later changed the questioning method, not directly handing over the old essay, but asking a few details. The puppet still appeared overly familiar. Only then did the teacher become nervous: an outsider does not need to obtain the original text to guess from the responses whether a certain article has entered the training book.
The teacher first thought the puppet was clever, able to guess the author from the writing style. The examiner then brought ten unfamiliar essays, and the puppet showed the same confident expression for only two of them, and could even name the crossed-out metaphors. That was not ordinary judgment; it was more like it had repeatedly seen these papers in class.
When the private school remediated the issue, the teacher first ordered the puppet not to recite the original sentences. But the puppet would still leak when questioned: it was more confident about articles it had seen and vague about articles it had not. Later the private school stopped casually feeding students' original drafts to the puppet, and when answering questions it also checked whether the puppet exposed that a certain article had once appeared in the book chest. The examiner finally reminded the teacher that leakage did not necessarily mean reciting the entire article. Sometimes just unusual certainty, special details, or familiarity with an old piece of writing was enough for others to guess whose text had entered the book chest.
Only then did the gentleman understand: even if outsiders cannot hear the original text, as long as they can determine that a certain private document once entered the training book, privacy has already leaked.