Take a look at the image below.
Would you believe that the four squares above are moving at exactly the same constant speed? There’s no bouncing or shifting, as there appears to be.
It’s the contrast of the lines, and the two separate colors that make them look desynchronized. Our brains have a tough time seeing the yellow edges against the white and the dark blue against the black.
In reality, it’s all an optical illusion. When the squares get close to each other your brain realizes they are moving at the same speed.