In France, apparently, there is one April fool's joke. Prepare yourself for this.

Oh what an hilarious jape.

Before I tell you, make sure you put on some tight clothing or some such to ensure you don't split your sides.

Ready? OK.

Every April first they put a paper fish on each other's backs. And laugh heartily.

That's it.

That's the French April fool joke.

So ubiquitous is this humour, the day is called, not April Fools, but 'poisson d'Aprile'.

Maria came home yesterday. April second.

She produced a piece of paper and asked me to show her how to draw a fish. I saw her concentrating very hard with a pair of scissors. Then she came up to me and said 'Dad you've got something on your back!' And craftily sellotaped her handiwork on in a way I would not have noticed at all if I had been unconscious. Maria and Carlo manoeuvred around behind me, pointed and giggled and slapped each other with pleasure.

Later when Mummy came home the kids greeted her with a furtive hug from behind. After a few minutes I pointed to Mummy's back and said 'oh look, there is a fish on your back.' I may have said it in the flat inevitable monotone of the straight guy setting up the zinger.

"Oh what's this? Who put this fish here?"

Maria, whom I think we can now agree is fully French, laughed so much she actually fell off her chair. We will have to sew up her sides.