The red button adds/removes half of the background grating. The swimmers bob up and down when they are in front of the grating but not when they are in front of a uniform background
Read more about the illusion and possible explanations
The red button adds/removes half of the background grating. The swimmers bob up and down when they are in front of the grating but not when they are in front of a uniform background
Read more about the illusion and possible explanations