Today isn't April Fools' Day.
Yes, the date (April 1st) is right, but here in England April Fools' Day only lasts until midday, so today is, strictly speaking, April Fools' half day.
Aprils Fools' Day has been around for so long that no one is quite sure when or how it started, but Iran's Sizdah Bedar has involved jokes played on the 1st or 2nd April ever since 536 BC.
In Italy, France and Belgium, people take the opportunity to tack paper fishes on each other's back and shout "April fish!"; in Flanders children lock out their teachers or parents, demanding treats as payment for readmittance.
But in English-speaking countries we're really talking mind games.
One of my favourite tricks was played on 1 April 1698, when several people were persuaded to make a trip to the Tower of London to see the lions washed.
Then, in 1976, there was the Jovian-Plutonian gravitational effect. The greatly respected British astronomer Sir Patrick Moore told listeners of BBC Radio 2 that the alignment of the planets Jupiter and Pluto planets was going to cause an upward gravitational pull. This would mean that people would be quite a lot lighter at 9:47 am. He invited his audience to jump in the air and experience "a strange floating sensation". Dozens of listeners phoned in to say the experiment had worked.
Good, eh? Except that now you are left with a problem. Are those two stories I've just told you true, or have I made them up as an April Fools' trick?
As there's nothing I can say at this point to convince you one way or the other (though they are actually both completely true) I think I'll go off and tell my husband about the pig sitting in our pond.
I bet he'll look, too.
Thing Not To Do Today: be a fool. The word fool comes from the Old French fol, mad person, from the Latin follis, empty-headed person, from the Latin word for bellows.