Here’s a little prank you should try — I have done it for decades, using it to entertain children and adults alike. It is all about presentation, and this is a slick version that always works.
This is how you start: choose a victim and ask her (or him) whether she thinks she can avoid saying a certain word for one minute. “I don’t understand — which word?” she replies. “Oh, any word we decide on. You must simply avoid saying that particular word for one full minute, for sixty seconds. Do you think that is possible?” This sounds preposterous, and your subject agrees that it should be trivially easy. “Which word?” she asks. You look around the room, at the light, a plant, a mug, a clock, and then you say: “Okay, let’s take a number: thirteen. Can you avoid saying it for a whole minute?” Puzzled look.
You look at your watch and say “We start now — the second hand is on ten. Okay, how much is two plus two?” — “Four?” your victim replies. “Plus four?” you continue. “Eight.” — “Plus seven?” There is a short pause: we’ve got to be careful. “Fifteen.” — “Times two?” This time there is a slightly longer pause, and your friend says, somewhat gingerly: “Thirty?”
Now’s your moment: “See!” you say, triumphantly. You lasted only 25 seconds! I told you you couldn’t do it.”
What follows it inevitable: your subject yells: “No, you said thirteen! THIRTEEN! Not thirty. You clearly said thirteen!” And you reply: “Now you have said it, after just 30 seconds!!” And your subject goes to the nearest wall and starts banging her head on it. That is what Petra, a backgammon champion, did when I pulled the prank on her. And Raghavi, an international chess master, shrieked in anguish. Later that evening she gave me an affectionate look and said: “I really hate you, Frederic.”
The prank works on kids too, beautifully. I tried it on my usual logic pal, grandson Enders, when he was five years old. Only he could not add properly yet, so we agreed that he must not say the word “mouse” for a full minute. I asked him what he saw when he was in the garden, and he replied trees, the lawn, the trampoline, the house… “There, you said it!” I said, and Enders yelled back: “No, you said mouse! I was not supposed to say ‘mouse’.” And I pulled the “Now-you-said-it” thing on him.
But then Enders did something truly extraordinary, something none of my adult victims had done. “No,” he said, “the game was over. I said it after the game was over!” We spent some time discussing: he contended that when I said he had used the forbidden word, the game was over, and we were discussing the (wrong) result I had given him. I maintained that the “game” was simply that he should not say the word “mouse” for a full sixty seconds, whatever transpired. It was grounds for vigorous debate, on the meta-level, and the five-year-old was arguing with someone who had studied philosophy and logic at university. Little Man Tate?
An addendum: Enders’ father Martin (who is pictured in the above philosophy story) witnessed me pulling the trick on Raghavi, and suggested I go further: “Tell them they should not say the word for one full minute, while you try to trick them into doing so.” That is painfully explicit. I tried it a few days later, and the subject became extremely cautious. He actually avoided “thirteen” for the full minute, saying “That was not the word we agreed to!” I don’t know if the announcement that I would be trying to trick him put him on his guard, or if he was generally very clever and attentive. I will try it on a few more victims before I draw any conclusions.