A patient hints at a strange realisation they had recently. Before revealing the answer, decide how you would interview them to establish whether this was a delusional perception.

Ask them to describe exactly what they perceived first, and then exactly what it made them realise, taking it slowly and in sequence. Listen for a sudden jump in logic rather than a chain of reasoning — a secondary delusion usually comes with an explanation the person can walk you through, while a true delusional perception does not. Ask specifically when the realisation happened relative to the perception: true delusional perception is essentially instantaneous, with no gap for reasoning to occur in.