Two Arches
Two curved shapes, one above the other. One of them is bigger — or is it?
How to play
Look first, then answer
Two curved shapes, one above the other. One of them is bigger — or is it?
- Under a minute · one question · then the explanation
How it works — best read after you have tried it
Comparing the nearest edges
The two shapes are identical. Where they meet, the short inner edge of the top one lies right next to the long outer edge of the bottom one, and it is those two neighbouring edges the eye compares — so the bottom shape wins, and swapping the two makes the other one win.
The American psychologist Joseph Jastrow published it in 1889; he is also known for popularising the duck–rabbit picture. Toy railway tracks and biscuits show it off well.