Farming the future

A duck, a horse and a chicken walk onto a farm… sounds like the start of a bad joke but it’s actually the start of a bit of mind mystery as you accurately predict the order your spectator will line up the animals in advance.

Language, ambiguity and a few farmyard animals

This trick relies on the ambiguity of human language, something computers hate. Computer languages need to be precise, saying exactly what needs to be done and when. We humans have languages that are open to interpretation – sometimes its not quite clear what we mean. Sometimes we take a guess.

On with the trick. The farmyard setting is just a fun way to present. It also allows us to introduce a very natural-seeming but constrained vocabulary. "duck", "horse" and "chicken" aren’t chosen at random. They are chosen because these common words have particular numbers of letters. "Duck" has four, "horse" has five and "chicken" has seven. That’s important, as we will see.

The set up

To perform the trick, first tear a bit of paper into three bits and sketch on them your most artistic rendition of a duck, a horse and a chicken. Pass these drawings to your spectator. Then take another slip of paper and, without letting your spectator see it, write on it (in order) the words "chicken", "horse" and "duck", or perhaps even just C, H, D. Put this slip of paper face down with "chicken" closest to you. This, you say, is your predication.

Ambiguity one: flip it your way

Let’s look at what’s on the table. If you turn the slip of paper over from top to bottom, then the word "chicken" (or the C) will be nearest to you, then H, then D. But if you turn the slip over lengthwise, the D will be closest to you, then H, then C. You never say which way you will turn the slip over and both seem totally natural. That ambiguity helps you make sure your prediction is right.

Ambiguity two: try persuasion

So all you need to do now is make sure that your spectator places the pictures in the order C H D or D H C, as you have both options covered. But how? You can set this up by telling your volunteer to start by placing the horse. After all, why not? Your spectator won’t know the rules, and if you fancy you could give them a story about how the horse wanders in first. You want that horse to be in the middle position so that the prediction slip works. Perhaps help steer your volunteer’s decision with a bit of language flim flam: remind them that in this trick you’re trying to influence them, and that most people either put the horse furthest away or closet to you. That way you’re hinting without saying that it would fool you if they put it in the middle. In the end it is a genuine free choice – they can put the horse where they like. You have to deal with a one in three chance they get it right.

If they do put the horse in the middle, great. Wherever they put the duck and the chicken won’t matter. At the end you just turn the paper over, either top-to-bottom or lengthwise, to show your predication is correct because of ambiguity one.

Ambiguity three: just spell it

In the worst possible case, they put the horse at one of the ends. Disaster? Don’t worry! That’s where the spelling comes in. In that case what you do add a new stage to the game, where the animals change position based on their spelling. Your volunteer won’t know that’s not how the game is played every time. You have three possible animal positions. Let’s call the position closest to you 'position 1'. If the horse is put in position 3, furthest away from you, spell out the letters of its name, bouncing back and forth between the two ends. So if the horse starts at position 3, the first letter, H, moves the horse to position 2. Then O takes the horse to position 1, R back to position 2, S to position 3, and finally E makes the horse finish at position 2, where you want it.

Similarly, if the horse starts at position 1, closest to you, H takes takes it to position 2, O to position 3, R to position 2, S to position 1, and E to position 2. Yes, the horse is back in the middle as required. You will need to spell out the other two animals, the duck and chicken, so as not to give the game away. But there are only two slots open – 1 and 3 – so they will always end up in a position where you can turn over the prediction slip to show the correct answer.

The computer science bit

This trick uses what a computer programmer would call an IF statement. IF (a particular thing happens) THEN (it triggers something else to happen). Here the trick has two ways to evolve. In one version the horse goes conveniently in the middle. The other version happens IF (horse not in middle) THEN (do the spelling bit). This sort of logical control is used all the time in computer programs, to account for different inputs. It’s often called 'branching', where the programme goes off down different routes depending on what the input is and what the rules are to process it. Branching is used a lot in computer games, often for non-player characters. Complex branching artificial intelligence can give them at least some feeling of intelligent behaviour. Of course, a character with fewer branching options is going to seem dumber. A one trick pony, you might say.