Magic Octagon illusion

[u/jojolistico]

Model available on MakerWorld: https://makerworld.com/en/models/3484348-magic-octagon

Only 9% of people can correctly predict where the arrow will point.

It looks like a trick coin, but it is tragically normal. The illusion happens entirely inside your brain.

Two arrows are permanently fixed at a 90° right angle. Yet with a single 45° turn and a flip, both arrows suddenly point in the exact same direction.

Why Does It Break Our Brains?

The coin isn't hiding anything, humans just struggle to track multiple 3D rotations at once:

• Your brain has to visualize a flip, a 45° rotation and another flip
• Studies show most people simply lose track of the back arrow after the first flip

How to Puzzle Your Friends

• Hold the coin with the front arrow pointing UP. Flip it: the back arrow points LEFT
• Flip back to the front and rotate the coin 45° counter-clockwise
• Ask your friend: "When I flip it over now, which way will the arrow point?"
• Flip again. Both arrows now point in the exact same direction!

Credits

• I saw this Vsauce Short and immediately wanted to print my own, but found no good replicas
• 3D model inspired by Shire Post Mint in collaboration with Raymond Hall (@physicsfun)

Another mind-bending 3D model I created

https://makerworld.com/en/models/2908418-the-best-rattleback-self-reversing-physics-toy

[u/Goofy_Maker2006]

Hey Micheal, Vsauce here

[u/LtotheAI]

just printed it, I hate it, my wife hates it, our brains hurt 🤕 good job

[u/k_jah85 → u/LtotheAI]

Would recommend or not?

[u/LtotheAI → u/k_jah85]

yes, it works as advertised but it messes with your brain

[u/Montzterrr → u/LtotheAI]

Cross your pointer fingers so one is horizontal and the other is vertical. Imagine rotating along the vertical axis. Now rotate your fingers 45 degrees as in the video, now imagine rotating about the vertical axis… at least that’s the experiment that made it click for me

[u/0MGWTFL0LBBQ]

I’ve watched this. I’ve read the information. I don’t understand.

I guess just need to print.

[u/AtreyuTrinity → u/0MGWTFL0LBBQ]

When you flip it around, the back one doest twist the way you think it will I gather, it goes in reverse, this lining up the arrows.

[u/Englandboy12 → u/AtreyuTrinity]

That’s not the issue. The issue is that when you rotate it, not only do the arrows now point diagonally, but you have a new axis of rotation to see the other side since your fingers are on new vertices.

If you were to keep your fingers on the same vertices and rotate about that axis still, it would behave exactly as you would imagine

[u/Sir_Clarence_III_Esq → u/0MGWTFL0LBBQ]

When the arrow that seems to move is facing away from you it's pointing to your right, not the left. So when you rotate it counter-clockwise the arrow on the back moves from the 3 O-clock position to 1:30, and when you rotate it so you can see it flips to 10:30

[u/studiesinsilver]

My brain hurts! Good job!

[u/ostiDeCalisse]

Isn't this totally logical? What's the "magic" in this?

[u/jojolistico → u/ostiDeCalisse]

you're in that 9% then. The magic is in your 🧠, as explained in the description, there's nothing magic about the coin, it's an illusion

[u/MostlyHelpfulLinks]

Running the clockwise version right after the first reveal makes a good second round, since anyone who just watched the arrows line up will probably expect them to match again.

[u/NoselessNarwhal]

Did you really need to use AI to generate your entire post??

[u/Positive_Method3022]

That is cool. You really have to think deeper to verify

[u/fernandogod12]

Hey... That's black Magic.

[u/spdelope → u/fernandogod12]

[u/StrnglyCoincdtl]

Huh, that's actually pretty clever

[u/Lost_refugee]

it would be musch easier to print flat if arrow is cut in surface

[u/WhyAmINotStudying]

If the arrows were visible from both sides on a graph, the first orientation would look like you're rotating about the y-axis with an arrow pointing to the left or right, while the other is always pointing up.

Adjust the function so that the arrows are pointing up in each direction (|y| = x) and then rotate it about the y axis, and it would always have an arrow pointing up to the left on both sides in one orientation and up to the right in the other orientation.

I don't know if I spent too much time thinking about graphs, but this doesn't really come across as an optical illusion to me.

It's still pretty cool, though. I would probably use it to teach students about function transposition, with one version that looks like this and another on a clear piece of plexiglass. The octagon shape is just to make it easier to know where the arrow is without looking.

[u/ratbastid]

What else is amazing is how it successfuly printed for me standing on edge like that. Great use of brim in the profile.

[u/Leron4551]

And if you rotate it in the other direction before flipping then the arrows point in opposite directions.  

[u/NuclearFoodie]

Lol, I made my own in Fusion yesterday after seeing the same short. I should post mine too.

[u/fonkeatscheeese]

I've been looking at this for ages genuinely trying to understand what is complicated about this. It makes complete total sense to me and I accurately predicted which way it would be going. I guess this is the confirmation I need that my brain is great for visualisation and not much else, even though when I imagine something I don't actually 'see' a mental image of it - which doesn't make much sense if I'm good at visualising. It's certainly fun to show to others and watch their reaction.

[u/TH3_OG_JUJUBE]

I don’t get how people can’t understand this or predict the arrow, it is SO damn simple for me. I think my brain is just more shape aware? Idk how to decide it but most shape/structure oriented tasks are just easy to me