I'm not typically a fan of posting random trippy videos I find on the Internet (I save those for the weekly acid-dropping/Enya-listening party I throw every Sunday). But this one was just voted the "Best Illusion of the Year" at a contest in which people vote for such things. And frankly, they were right--it's pretty badass.
The illusion was created by Harvard grad student Jordan Suchow and psychology professor George Alvarez.
Focus on the center gray dot and watch for when the colored dots stop changing colors.
The colored dots are in fact changing the whole time, it's just that when they move back and forth the motion confuses the senses into thinking that the colors aren't changing.