A patient reports both an unusual taste and an unusual smell with nothing present to account for either. Before revealing the answer, decide what distinguishes a gustatory hallucination from an olfactory hallucination.

Ask specifically which sensory modality, taste or smell, is affected, since the two are often paired but remain conceptually distinct experiences. A gustatory hallucination is often paired with, but conceptually distinct from, an olfactory hallucination: it is specifically a taste perceived with nothing in the mouth to produce it, commonly metallic, bitter, or otherwise unpleasant. An olfactory hallucination is specifically a smell perceived with no external source that could explain it, most often unpleasant, such as burning, decay, or sewage, though pleasant odours are also described. Because taste and smell interact so closely, both may be present together, but which specific sensory channel, mouth or nose, is affected distinguishes the two.