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Dad always said that laughter is the best medicine, which I guess is why several of us died from tuberculosis.
— Saturday Night Live · Deep Thoughts by Jack Handey
Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker repeats a father's cheerful saying that laughter is the best medicine, then undercuts it with a grim punchline. Since several relatives died of tuberculosis, the saying evidently did not cure anything. The humour is deadpan and dark, mocking comforting advice by showing its deadly consequences.
Context reviewed