Here's how Ninio describes how the illusion manages to fool your eyes and brain, per the abstract from a scientific paper published back in October of 2000:
"When the white disks in a scintillating grid are reduced in size, and outlined in black, they tend to disappear. One sees only a few of them at a time, in clusters which move erratically on the page. Where they are not seen, the grey alleys seem to be continuous, generating grey crossings that are not actually present. Some black sparkling can be seen at those crossings where no disk is seen. The illusion also works in reverse contrast."
The illusion soared in popularity on Reddit on Monday after it was shared by game developer Will Kerslake via Twitter on Sunday night and Japanese psychology professor Akiyoshi Kitaoka via Facebook on Sunday morning, according to a report by BBC.