Read the excerpt from Mark Twain's "The £1,000,000 Bank-Note". Well, I was perfectly honest and square with her; told her I hadn't a cent in the world but just the million-pound note she'd heard so much talk about, and it didn't belong to me, and that started her curiosity; and then I talked low, and told her the whole history right from the start, and it nearly killed her laughing. What in the nation she could find to laugh about I couldn't see, but there it was; every half-minute some new detail would fetch her, and I would have to stop as much as a minute and a half to give her a chance to settle down again. Why, she laughed herself lame--she did, indeed; I never saw anything like it. I mean I never saw a painful story--a story of a person's troubles and worries and fears--produce just that kind of effect before.

Which rhetorical device is demonstrated in the excerpt?