In this instance it was wayward ink. I had just cleaned my fountain pen and had installed a new ink cartridge. Since the nib and feed were completely dry I was shaking the pen to encourage ink flow. But I was doing this over my journal and, wow, a big, blue blob of ink magically appeared. Oy.
My recovery was this:
|"Ink Blot Birds"|
I am adhering to the art journaling precept of "there is no-such-thing..." :-)