By exploring memory mismatches, hidden spatial patterns, and the brain’s internal fact-checking system, researchers are discovering that déjà vu may reveal how the mind constructs reality itself. You walk into a room you have never seen before. The sunlight hits the floor at a strange angle. Someone laughs in the corner. A chair scrapes softly against the ground. Then suddenly, a wave of certainty crashes over you: this has happened before. For a few seconds, your mind become