A strange optical illusion called “Benham’s disk” has been making the rounds online this week. (You can see the illusion here.) Here’s how it works: After watching this short video of a spinning disc, some viewers report seeing colors (though people report seeing different colors, the image is black and white). Some see no change at all. The strangest part of the Benham’s disk illusion is that scientists aren’t exactly sure why it works. Some have theorized that it affects the eyes internal cones that interpret the wavelength of light; others say the spinning motion deactivates certain cones in the eye. If Kramer taught us anything, it’s to not get our rods and cones all messed up …