A schoolgirl, stripped, bound to a chair, gagged and anesthetised, whimpers in terror as the filthy curtains surrounding a four-poster bed begin to part.
Is this all a bit of a con? Warning: contains spoilers for Inside No.
Fear and laughter are proper physical reactions in people, rather than intellectual ponderings.
You want to incite those reactions and you do that by getting ahead of the audience and not letting them get ahead of you.