Every line in one color: the same smooth wave in every row.
Straight, bent or tilted?
Curvature blindness
Some of these lines are smooth waves and some are zigzags with sharp corners. Which are which?
Every line is the same smooth wave. Only where it changes from light to dark is different.
Why? Where the color changes at the top and bottom of each wave, your brain takes the change for a corner, and the gentle curve is lost. Kokichi Takahashi found this in 2017; this is our drawing of it.
Picture: Drawn by Science Playground, after Kokichi Takahashi