Stare at the object and see if it beings to move and shimmer.
If you focus on the outermost groove, it will become projected as your eyes follow it around the wheel.
This optical illusion, as the traditional spiral, is a popular way of tricking the mind. The black center gives us a focal point, but when we fix upon it, the squiggly black and white lines behave erratically around it.
Our brains cannot lock these down, as they grow smaller towards the center, giving the illusion of perspective, and so in our minds they being to move and shimmer.