There's nothing unique about the tradition that you don't reveal whodunnit in The Mousetrap

Much is made of Mousetrap omerta - the taboo against revealing the identity of the murderer in Agatha Christie's record-breaking play. But it never used to be a unique tradition.

Whodunnits were one of the staples of weekly repertory theatre, and it was common for such plays to end with one of the cast saying something like:

"We hope you enjoyed the play and will tell your neighbours about it - but please don't tell them who the killer is."

An example of this comes in one of the funnier anecdotes in David Hemmings' memoirs.

The summer of 1960 saw him in rep at Ryde on the Isle of Wight. This doesn't sound like the top of the tree for a young actor, but he was 18 and wanted to be with his first wife Jenny Lewes. This newspaper cutting comes from that summer. 

To make the sometimes very ordinary plays more fun, the cast had evolved a game where they had to pass an apple to each other without altering an action of the play. So if you had the apple, passing a letter to another actor would present a perfect opportunity for getting rid of it. And the actor left with the apple at the end of the play had to buy the first round of drinks.

In one performance of a whodunnit, Hemmings was the detective. Alone on the stage with the victim's corpse, which was under a sheet, he was giving the final speech, explaining how the murder had been done. As the corpse had the apple, he reckoned he was safe.

Suddenly, the corpse reared up, dragged itself across the stage issuing horrible guttural noises, passed the apple to Hemmings under cover of the sheet and then died again at his feet.

After that, says Hemmings, it didn't seem worth asking the audience not to reveal the ending of the play - it would never end that way again.

If you do want to know the murderer in The Mousetrap, there's Wikipedia. Or you can listen to Tom Holland blurt it out in one of the better editions of The Rest is History.