Your eyes collect light, but your brain builds the picture, and sometimes it gets things gloriously wrong! Explore 25 original illusions: impossible shapes, secret 3D pictures, brain tricks and things that move when they don't.
Be gentle with your eyes: try for only a minute at a time, and stop if your eyes feel strained, sore or tired. Some people can't see these at all, and that's okay too!
🏅 Reveal the trick (or open "Why it happens") on 10 illusions to earn the Illusion Master badge: 0 / 10
Try this: Look at the left end: three round prongs. Now slide your eyes to the right end: only two square bars! Try to count the prongs in the middle…
Your brain reads each end as a real 3D object, and both ends make sense. But the same lines are used for different edges, so the middle can't exist. Your brain checks small pieces at a time and doesn't notice the fight until you look at the whole thing.
Try this: Follow one beam with your finger around the triangle. Does it go up? Down? Every corner is a perfect right angle… so how does it join up?
Each corner is a normal L-shaped corner. Put three together and they can't really close into a triangle in 3D! This one was drawn from a real 3D shape that does NOT join: one end is far away and hides perfectly behind the other. From exactly one viewpoint, the gap vanishes.
Try this: Cross your eyes until the two yellow dots become three, then focus on the middle one. Which shape floats closest to you? Which one sinks behind the frame?
Your two eyes see from slightly different spots. Your brain measures how far each thing shifts between the eyes (called disparity) and turns it into depth. Here each shape is shifted by a tiny different amount, so your brain builds a 3D scene!
Try this: Cross your eyes so the two cubes merge into one in the middle. Hold it steady… the cube should pop out like a real wire frame!
Corners that are closer to you are shifted a little more between the two pictures. Your brain uses those tiny shifts to work out which corners are near and which are far.
The secret shape is a ⚡ lightning bolt! In the right picture, the dots inside the bolt are slid sideways by just 4 dots.
Try this: Two pictures of TV static! Cross your eyes until they merge. Wait a few seconds… something hidden should rise out of the dots. Press 🔀 to make new dots.
Neither picture has a bolt in it on its own. The only clue is that a bolt-shaped patch of dots is shifted between the two. Your brain matches millions of dots and finds the shifted patch, so ONLY your 3D vision can see it. Spies once used tricks like this to find hidden things in aerial photos!
Try this: Cross your eyes to merge the rings. Is it a cone pointing at you, or a tunnel going away?
The small rings are shifted outward more, so your brain thinks they are closer. Stack them up and you get a 3D cone sticking out of the screen.
Try this: Which line is longer: the top one or the bottom one?
They are the same length! Fins pointing out make the line look like the far inside corner of a room (bigger), fins pointing in look like the near outside corner of a building (smaller). Your brain adjusts size for distance automatically.
Try this: Which orange circle is bigger?
They are identical! Your brain judges size by comparing to neighbours. Next to giants, you look small. Next to tiny friends, you look huge.
Try this: Are the grey lines between the rows tilted or straight?
They are perfectly straight and parallel! The shifted black and white tiles plus the thin grey "mortar" fool the edge-detecting cells in your eyes, so the edges seem to lean like wedges.
Try this: Look at the white crossings. Do you see fuzzy grey dots? Now look straight at one… where did it go?
Cells in your eye fight with their neighbours (called lateral inhibition). At a crossing there is more white all around, so the middle looks darker. Straight ahead your vision is sharper, so the ghost disappears.
Try this: Let your eyes wander over the grid. Do black dots blink inside the white dots?
There are NO black dots! The edge cells in your eyes get confused at the crossings, and when your eyes jump around, dark spots flicker in and out.
Try this: Do you see a bright white triangle on top? Trace its edges.
No triangle was drawn! Your brain hates gaps, so it fills in the missing edges to explain why the circles have bites out of them. It even makes the fake triangle look brighter.
Try this: Which square is darker: A (in the shadow) or B?
They are exactly the same grey! Your brain knows shadows make things darker, so it "un-shadows" A and sees it as a light square. Your brain shows you what things ARE, not the actual colour on the screen.
Try this: Are the long lines parallel, or do they lean towards each other?
They are parallel! The little crossing lines make your brain overestimate the angles, so the long lines seem to tilt in opposite directions.
Try this: Which yellow bar is longer: the top or the bottom?
Same size! The tracks look like they go off into the distance, so your brain thinks the top bar is farther away, and something far away that looks the same size must be BIGGER.
Try this: Trace the spiral to the middle with your finger. Where does it end?
Surprise: there is no spiral, only circles! Each little tile is twisted, and your brain adds up all those tiny twists into one big swirl.
Try this: Stare at the cube. Is the blue-ish front face at the bottom-left or the top-right? Wait… it flips!
The drawing works both ways, so your brain keeps switching between two answers. You can learn to flip it on purpose!
Try this: Is it a duck facing left or a rabbit facing right? Can you see both?
One drawing, two answers. Your brain picks one meaning at a time. Fun fact: around Easter, more people see the rabbit first!
Try this: Do you see a black vase or two yellow faces looking at each other?
Your brain decides what is the "thing" and what is the "background". It can only do one at a time, so the picture flips.
Try this: Look at the red dot in one wheel, then let your eyes wander. Do the other wheels seem to turn by themselves?
Nothing moves! Your eyes process dark and bright patches at slightly different speeds, so a repeating black→blue→white→cyan pattern looks like it slides, especially out of the corner of your eye.
Try this: Press start and stare at the centre for 20 seconds. Then look at your hand. Whoa! Does it seem to shrink or warp?
Motion cells in your brain get tired of seeing the same motion. When it stops, the cells for the opposite direction win for a moment, so still things seem to move backwards. This is called the motion after-effect.
Try this: Stare at the black dot for 20 seconds without moving your eyes. Then press the button (or tap the picture). What colours appear on the white?
Colour cells in your eyes get tired. After staring at green, cyan and yellow, the opposite colours (pink, red, blue) take over for a few seconds. That is a negative after-image!
Try this: Press start. Do the blue and yellow blocks walk step-by-step like feet, taking turns?
They move at the exact same steady speed! When a block's edge is over a stripe with strong contrast, it looks faster; with low contrast it looks slower. Press Reveal to remove the stripes.
Try this: Press start and stare at the black cross for 15–20 seconds. Do you see a GREEN dot running around? Do the pink dots fade away?
There is no green dot! The gap where a pink dot vanishes makes a green after-image. Staring makes the steady blurry pink dots fade (Troxler fading), so only the green ghost is left.
Try this: Stare at the little cross without moving your eyes for about 20 seconds. What happens to the fuzzy blobs?
Your eyes stop reporting things that never change, especially blurry things in the corner of your eye. Move your eyes a tiny bit and BAM, they come back!