The blue and yellow bars are moving at the same constant speed. They are not starting and stopping. Check the code if you don't believe me! You can also click the Stage to make the stripes disappear and reappear.
The illusion is usually called the Stepping Feet illusion or Footsteps illusion. It was originally demonstratedby Stuart M. Anstis, a vision scientist at UC San Diego in “Footsteps and inchworms: Illusions show that contrast affects apparent speed” from 2001.
