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Over on Quora, users asked for a brain teaser that is very short and extremely hard for adults.
They received an excellent answer from Peter Flom
Brian Hoang has also suggested this puzzle, which he claims was shown to him by a waiter in a Mexico.
The puzzle uses 12 tooth pics, arranged to create four squares:
The challenge? Turn this shape into three perfect squares, in exactly three moves.
Once you've had a bash at this for over 30 minutes to no avail, scroll down to see the three moves:
Can you find any other solutions? Let us know in the comments.