A patient reports hearing voices. You want to check specifically whether this might be a functional hallucination. Before revealing the answer, decide what you would actually ask.

Ask whether the voices seem to need something else happening to set them off: "Do the voices only happen when a particular sound is going on, like the tap running or the television?" Confirm that the real, triggering sound is heard accurately and not distorted, since accurate perception of the trigger is what separates this from an illusion. Then ask what happens to the hallucination when the trigger stops — a functional hallucination should stop with it.