I must be thinking of something else. There are circles that appear in grass
that looks like somebody took a little tiny fertilizer drop spreader and made
circles, resulting in much darker, greener grass in these rings. We have called
them Pixie Circles.

BTW, don't use those Areaters that you put on your feet like old time
rollerskates. They have spikes on the bottom. Not only do THEY NOT areate the
soil, they do the opposite, the compact it more. And if you do it enough,
you'll eventually fall and break or sprain your ankle.