Elaine, Lois (not her real name), and I went to see a film. Then we went out for a meal. Lois has an arts degree from the University of Oxford, which means that she can tell you everything you need to know about the influence of post-modernism on Latin-American literature in the final quarter of the twentieth century, but she can’t add up.

Lois: Here’s my share of the meal. [She passed over two £20 notes.]

Elaine: [passing them back] No, this is our treat.

Lois: No. You overpaid by £10. [Passing the money back]

Elaine: No we didn’t, because you gave me the correct change. [Passing the money back. For me, it was like watching a tennis match.]

Lois: No, you need the money for the vet. [Passing it back.]

Me: [deftly intercepting the money and flicking it back with my best table tennis wrist movement6.] No, Elaine has already been wormed.

The two ladies were in hysterics. By this time my forehead was on the table.

Me: Call the waiter and ask him if he’s got one of those big knives, the ones people use for harakiri.

Afterwards, I emailed Lois a link to a helpful maths video:

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