The stripes taken away: the two blocks glide side by side at one speed.
Tricks of motion
Stepping feet
Do the two blocks take turns stepping forward?
No: they move at a steady speed, side by side.
Why? Over the stripes, each block’s edges keep disappearing and reappearing. Your brain judges speed from the edges, so it sees each block speed up and slow down.
Picture: Drawn by Science Playground · Wikipedia(opens in a new tab)