Magic Octagon Illusion Coin — Arrow Flip Brain Teaser
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An arrow on each side, always 90° apart. Turn it 45° before spinning it and the back arrow lands where nobody expects.
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Updated at source:
Model information
- Source
- Printables
- Category
- Puzzles & Brain-teasers
- License
- Creative Commons — Public Domain
A printable take on the classic Magic Octagon brain teaser. Each face has an arrow and the two are always 90° apart — yet turn the coin 45° and spin it over, and the back arrow points the same way as the front, or the opposite way, depending on which way you turned it.
See it in action: The Magic Octagon — Vsauce
How to perform it
Pinch the coin by its top and bottom points with the front arrow pointing up. Spin it left to right: the back arrow points left.
Spin it back, turn it 45° counter-clockwise (arrow now up-left) and ask where the back arrow will point. Most people say down-left. Pinch the new top and bottom points and spin: it points up-left — the same way as the front.
Start again, turn it 45° clockwise (arrow up-right) and spin: the back points down-left — the opposite way.
Why it works
Spinning about a fixed axis mirrors the back arrow across that axis. Turning the coin moves the front arrow one way but the spun back arrow the other way, so a 45° turn changes the gap between them by 90° — from 90° to 0° or 180°. Our brains expect the 90° to stay put.
Credits & history
Based on the Magic Octagon coin from Shire Post Mint, designed by Raymond Hall (@physicsfun), whose Instagram post popularized it.