This one arose from a splatter of paint while clearing out the last vestiges of color from an airbrush. I typically use scrap paper for that, which you can see below in an example I fished from my wastebasket.
While working on something else, the scrap paper stayed in my peripheral vision. I kept glancing at it, imagining a distorted face with coral-like formations arising out of it.
Finally I gave in to temptation and took a few minutes to define the image I was seeing in my head a little better, using extra of the paint I had started with—a mixture of Liquid Carbon Black and Raw Umber [Golden paint company]. I scratched out highlights with the brush handle, later supplementing those marks with white and a touch of yellow off another palette I had going.