Try to keep these balls in the center of your vision, they'll keep moving!
What: This isn’t the first time we’ve got some Akiyosi Kitaoka  on the site, and it won’t be the last. This is a classic example of illusory motion, where the balls appear to be moving in the peripherals of your vision, but are in fact completely still.
How To: Mix up the colors, sizes, and spacing to see how it affects the illusion. I found that the illusion is strongest when the colors are contrasting, and the balls not super large, although I could see it there
Explain it: Another Illusory Moment, and as always the Wikipedia  has a great description of the current thought process. I’ve also mentioned within the illusory motion beans illusion how this is working (as I can understand it), your brain is used to perceiving things that fade one way or the other as moving, and the contrasting colors here are causing a collusion of the senses.
I've researched these illusions in my spare time but am clearly not any kind of expert and my explainations are pretty smooth brained, if you find something mis-cited, earlier examples, or general mistakes please new let me know via email@example.com, be kind!