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This is an archived version of the 2026 Key Clues Challenge website. For information on the upcoming event, visit keyclueschallenge.uwaterloo.ca.

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Solution: Ambidextrous Hexatetraflexagon
Answer: OBTUSE

As the title suggests, this is a hexatetraflexagon, something you cut out and fold. Here is a link to a helpful video about the hexatetraflexagon: https://www.youtube.com/watch?v=7H4lDi79YY8.

A flexagon like this can be folded in two ways (hinted to by the 'ambidextrous' part of the title), each a mirror image of the other. You can either construct it by folding it in a clockwise direction, or in a counterclockwise direction. Building it one way and then flexing through the possible states, you get the pink letters. Building it the other way, you get the dark-blue letters.

To disambiguate, if you're looking at the letter as intended, a complete circle of the same colour appears at the center of the square, and a number of the same colour appears in the top-left corner (giving you the orientation with which to look at the letter)

Parts of the flexagon that are both pink and dark blue, are a sort of medium purple colour.

Equipped with all this information, you flex your way through the flexagon, finding 12 letters (as shown in the pictures). Ordering the letters by the number that appears in the top left, you get WITLESSANGLE.

The puzzle comes with the message "What do you call a ... ? (6)". Inserting "Witless Angle" where the ellipses are, gives the clue:

What do you call a witless angle? (6).

The answer is OBTUSE.

Author’s Notes

This puzzle was one of the last to be written. Before it was written, the competition didn't have any foldy-bendy puzzles (a technical term), and I had never written a foldy-bendy puzzle before. It seemed like I could avoid the challenge no longer!

A couple of years ago, one of the Enigmatologists made an offhand suggestion that next time we should make a word search on a flexagon. Over the holidays I watched a couple of videos about flexagons (because, you know, we needed a foldy-bendy puzzle) and then wrote Ambidextrous Hexatetraflexagon. I chose this particular flexagon because no gluing was needed (you're welcome!). It was super duper enjoyable to make, and I hope you enjoyed it too!