You suspect an organic hallucination in a patient. Before revealing the answer, decide how you would assess for this.

Take a careful history and examination looking for an identifiable physical or neurological cause, since this, rather than the perceptual quality of the experience itself, is the defining feature. Ask specifically about limb loss or congenital absence if a phantom limb presentation is suspected, including the character and location of any sensation, and whether pain is present. Look for other signs pointing to the underlying physical condition, such as fluctuating consciousness or focal neurological findings. Establish that the hallucination is not specifically and reliably triggered by, and dependent on, a real concurrent stimulus in the same sensory channel, which would instead point toward a functional hallucination.