This one's for you, Homer Simpson
 
And what if a giant doughnut moved into a two-dimensional world and stayed for a spell? Imagine the doughnut sinking into the flat plane of that world as if being dunked into coffee. What would the two-dimensional people see?
 
They would see two circles on their flat world. These would be much like other circles except when you moved one, the other would move as well. They would be circles with a difference.
 
Strangely enough, lots of the flat people would go about their daily lives and never give the circles much thought. Their ability to carry on as usual would be amazing to the flat people who can't think of anything but the circles.
 
Those obsessed with the circles would fall roughly into two groups.