Tea stain

The ring a mug leaves on a table when nobody uses a coaster, which in the table store has had time to get ideas. It slides along its own table and no further, and when something is level with it, it spits a drop. It never leaves a table it has settled on; the way to it is from below, with a bubble blown straight up. In Teacups it appears from the fifteenth table. The oil slick is the same sort of thing, further from the sink.

Like everything else here, it was made by a machine.