How to do the twenty-card trick: Mutus Nomen Dedit Cocis

Deal twenty cards into ten pairs and let someone remember one pair. Gather the pairs, then deal them into four rows of five, secretly following four Latin words: MUTUS, NOMEN, DEDIT, COCIS. When your helper tells you which row or rows hold their two cards, the words tell you exactly where they are. No sleight of hand, no memorised deck, just a grid you carry in your head.

This is a classic self-working card trick, and a satisfying one to learn, because once you understand the grid you can never forget it. It works for one helper or for several at once, and it suits a table at home or a games night.

What does the audience see?

You deal twenty cards face up in pairs. While your back is turned, a helper looks at the pairs and remembers one of them, both cards. You gather the cards, deal them out again into a neat grid and ask one question: “Which row are your cards in?” They might say one row, or two. You immediately point to both of their cards.

What do you need?

• Any ordinary deck. You only use twenty cards, so pick twenty that are easy to tell apart.
• A table with room for four rows of five cards.
• Four Latin words memorised: MUTUS NOMEN DEDIT COCIS.

How does the grid work?

Picture the four words written one above the other. Each word has five letters, so together they make four rows of five positions:

Row	1	2	3	4	5
1	M	U	T	U	S
2	N	O	M	E	N
3	D	E	D	I	T
4	C	O	C	I	S

Look closely and you’ll see that the grid uses exactly ten letters, and every letter appears exactly twice. Ten letters, ten pairs. Each pair of cards is dealt onto the two positions that share a letter.

How do you do it, step by step?

1. Deal ten pairs. Deal twenty cards face up on the table in ten groups of two.
2. Let your helper choose. Turn away and ask them to look at the pairs and remember one pair, both cards. With a group, several people can each remember a different pair.
3. Gather the pairs. Pick up the pairs one at a time and stack them, so that the two cards of each pair stay together. The order of the pairs doesn’t matter.
4. Deal the grid. Holding the stack face down, deal the cards face up into four rows of five, following the letters. The first two cards go on the two Ms. The next two go on the two Us. Then the Ts, the Ss, the Ns, the Os, the Es, the Ds, the Is and finally the Cs. That order is simply each new letter as you read the words left to right, top to bottom: M, U, T, S, N, O, E, D, I, C.
5. Ask one question. “Are your cards in one row, or in two different rows? Which ones?”
6. Reveal the cards. Use the table below to find the letter, then point to the two cards on that letter.

How do you find the cards?

Your helper says	The letter
Only row 1	U (the two Us in MUTUS)
Only row 2	N (the two Ns in NOMEN)
Only row 3	D (the two Ds in DEDIT)
Only row 4	C (the two Cs in COCIS)
Rows 1 and 2	M
Rows 1 and 3	T
Rows 1 and 4	S
Rows 2 and 3	E
Rows 2 and 4	O
Rows 3 and 4	I

You don’t need to memorise this table. Each word has exactly one letter that appears twice inside it, and any two words share exactly one letter. So if they name one row, find the doubled letter in that word. If they name two rows, find the one letter both words have in common.

Why does it always work?

It’s pure bookkeeping. Because you deal each pair onto matching letters, the letter tells you where both cards are. Because every possible answer (one of four rows alone, or one of six combinations of two rows) points to a different letter, there’s only ever one place the cards can be. Ten answers, ten letters, ten pairs. Nothing can go wrong as long as you deal in the right order.

How do you make it look like magic, not maths?

• Deal casually. Practise until you can deal the grid at an even pace without pausing to think. Saying the words silently as you deal helps: “M, U, T, U, S…”
• Don’t stare at the grid. Glance at the rows they name, then look at your helper while you “read” their mind.
• Use several helpers. With three or four people each remembering a pair, finding them one after another builds the trick.
• Repeat with care. The grid gives the same answer every time, so doing it twice for the same person can let them spot the pattern.

Is there an English version?

Yes. Any four five-letter words that use ten letters twice each, with one doubled letter per word and one shared letter between every pair of words, will work. An article in Word Ways (1994) gives the English set BIBLE ATLAS GOOSE THIGH. Check it against the rules above and you’ll see it works the same way.

What helps you take it further?

• Mathematical Recreations and Essays by W. W. Rouse Ball is a free 394-page PDF of mathematical puzzles and amusements, including arithmetical card tricks, from the tenth edition of 1922.
• Tricks with Cards by Professor Hoffmann is a free 148-page PDF covering the principles of sleight of hand with cards, then tricks without apparatus and tricks with prepared cards.

Need a fresh deck? Browse our playing cards. For more self-working card magic, try the 21-card trick and the key card trick.

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