As an area of the cracker cooks, it bubbles up in just a few seconds, leaving clear marks as to where there is microwave power and where there isn't. For this particular microwave, Saturn-shaped objects will cook evenly.
Obviously what is happening is that there are two hotspots in this microwave: one in the center, and one offset from center which traces out a circle thanks to the rotating plate in the bottom.
And then, like any good scientist, she recreated the entire experiment in four other microwave ovens to see if the results could be duplicated. Link