Follow the red dot with your gaze (head rotation helps). Observe that some of the squares in the background seem to shift. The effect is fleeting for me – sometimes strong, sometimes missing. But all motion here –apart from the red dot– is illusory.
With the popup menu, select
Lanes rather than
Circle. Many more settings wait for you to play with them (“Ranomize” is not useful yet).
This is a variant of the Pinna-Brelstaff illusion which already appeared in their 2000 paper. The same explanation applies.