How Many Boulders Are There?

how many rocks optical illusion
How Many Rocks Do You See?

Now this is an interesting find! Aihira Kenji, the one responsible for Rope Illusion and Football Player Stereogram, created this fine little animated gif file. The game is simple – All you have to do is count how many boulders are present inside the picture.  Is it 9? No, wait! There are 10! No, wait…I give up. Can you at least spot when or where does the extra boulder appear/disappear? If you stare at the animation for a while, solution becomes obvious.

Remember those nervous Leprechauns? They pulled the exact same trick back in the old days! If your memory serves you well, you’ll remember we had Mandarin warriors and Mad Scientist’s Soccer Team that did the same.

No matter how much experience I have, and how long I have stared at those previous animations, I never had luck with them. Just like my troubles with seeing stereographic images. Perhaps some people are born to see them, and some not. Enjoy our newest addition!

how many rocks optical illusion

38 Replies to “How Many Boulders Are There?”

    1. i totall get it now. that bottom boulder is the magical “extra” boulder. but theres NO EXTRA. its just that they take the top part of every boulder, n for the bottom boulder, the “top part” is the whole thing! so it moves, and then theres no boulder where it was.

  1. I see. There’s no top piece to the bottommost rock, and no bottom to the one just to its right. When it turns, those line up, creating a space. Cool!

  2. If you look at the first picture, the secret lies in the bottom and bottom-right boulders. Each boulder splits into an “outside” and an “inside” section, except for these two. The “inside” section of the bottom boulder and the “outside” section of the bottom-right boulder are blank. When they merge, they create one “invisible” boulder at the bottom of the second picture. That’s where the 10th boulder went!

  3. There are nine, then ten, with the tenth one appearing at the bottom right hand corner. I think. It’s really hard to tell because they are moving so fast. Even your stills don’t give the answer. Good illusion, yes indeed, yes indeed.


    The one closest to the bottom is a rock itself, with all parts on the outer ‘ring,’ which then moves and lines up with the parts of the rock next to it. Same goes for the one to the right of the bottom-most rock… Almost. It’s a small rock, with all parts on the inner ‘ring,’ so when the piece from the other rock lined up, it made a bigger rock.


  5. It’s not that complicated:
    First there are two pieces “stand alones”. One of them is a moving piece, the other one not (the two pieces at the bottom of the picture, next to each other). When the objects turn round, both stand alones were combined with another brick-piece. The result is that you count at least one brick less. Sorry for the bad english ^^

  6. There is no extra boulder. Basically when moving one item around, around 10% of one boulder gets added to next one. 20% of second one goes to next one and so on… in the last case, 100 % boulder gets added to the next one… So, it looks like one has disappeared.

  7. I think this is the best understandable explanation:

    There are 17 boulderparts.

    In the left picture, 14 are combined to 7 boulders, 3 parts are on their own which makes 10 total.
    In the right picture, 16 are combined to 8 boulders, 1 part is on his own which makes 9 boulders total.

    Your welcome! ;)

  8. the very last one, following clockwise when there are 9, doesn’t have anything removed from it.

    the graphics change their shape and shading as they join with the new ones… I didn’t know boulders could do that…. clay maybe, but not boulders P

  9. Those are Boulders? I thought they were potatos. Either way… there are 9 potatos…. And ten there are 10. Vodka anyone?

  10. A nice trick, though one that has been done before in other guises. A friend once sent me a similar illusion with a team of hairy men seeming to vary in mumber as they moved.

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