This puzzle is part of the Monthly Topic Challenge #8: Cellular Automata.

Find four capital letters that can replace the X's (and explain why).


  • 1
    $\begingroup$ two blocks leaning left / two blocks leaning left / my muscles, my muscles / involuntarily flex $\endgroup$
    – juicifer
    Mar 17, 2023 at 5:14

1 Answer 1


I think the answers are as follows

L. Two blocks leaning left
I. Four Blinkers
F. Honey Farm
E. Devil laughing on his side?

Notice how it spells


That's because

Each of the clues is describing a configuration in Conway's Game of Life. The clues represent the configuration that the game settles down to if we begin with a configuration described by the corresponding number or letter.

For example

If we begin with "2" given as follows,
enter image description here
after several generations, it settles down to become a "pair of boats"
enter image description here

Another example

If we begin with "E"
enter image description here
Then, after several generations, it settles down to become this
enter image description here
which looks like the devil on his side and the mouth is a blinker (suggesting laughing).

Try it for yourself

I've been using this site: https://playgameoflife.com/

Title Explanation (thanks to Amoz for drawing my attention)

"Two Blinkers, A Pair of Boats" correspond to the numbers 4 and 2 and 42 is The Answer to the Ultimate Question of Life, the Universe and Everything in The Hitchhiker's Guide to the Galaxy

  • $\begingroup$ Great! Bonus explain the title. $\endgroup$
    – Amoz
    Mar 17, 2023 at 12:23
  • $\begingroup$ @Amoz, good point, I totally overlooked this. Very nice puzzle! $\endgroup$
    – hexomino
    Mar 17, 2023 at 13:49
  • $\begingroup$ What's the significance of the position of each clue in the graphic in the question? $\endgroup$
    – Rosie F
    Mar 17, 2023 at 14:51
  • $\begingroup$ @RosieF This is probably incorrect, but rot13(Vg frrzf gb ercerfrag gur tevq va gur Tnzr bs Yvsr. Ubjrire, vs lbh chg gung cnegvphyne flfgrz vagb gur Tnzr bs Yvsr, vg qvrf bhg nsgre n srj gheaf.) $\endgroup$ Mar 17, 2023 at 16:01
  • 1
    $\begingroup$ @RosieF rot13(Gur pyhrf ner neovgenel ohg gur neenatrzrag vf n 13 cvkry qvtvgny qvfcynl gb thvqr ubj gb funcr lbhe punenpgref.) $\endgroup$
    – Amoz
    Mar 17, 2023 at 16:13

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