Inksplot, AKA Blot and *, is perhaps Gahan Wilson's best known short story, appearing first in 1972 in Harlan Ellison's Again, Dangerous Visions. You may recognize it under its actual title, which is something like:
^^^^^^^/\/\/\/\/\(███)/\/\/\/\/\/\/\^^^^^^
Well, sort of. It looks like an audiograph with an ink blot in the center. As far as I can find, there is no 'official' statement as to how this should be translated into English. The copyright information on its most recent appearance, in Unnatural Creatures (an anthology of stories selected by Neil Gaiman) lists it as Inksplot, although reviewers of Gahan Wilson's own collection, The Cleft and Other Odd Tales refer to it as Blot.
Reginald Archer is gentleman of some means, and he is somewhat uptight when it comes to appearance and cleanliness. He is therefor rather disturbed to find an unusual black stain on his tablecloth one morning, and has his butler remove it for cleaning -- only to find that it has transferred itself to the blotter on his desk. And no sooner than his butler removes the blotter, the splotch moves to the wall. And with each move the splotch grows bigger and more... tentacled. They quickly determine that it moves instantaneously each time they glace away -- or blink -- and that it grows larger with each move.
Things escalate.
The story is only about 15 pages long, and one and a half of those pages are illustrations. Of a blotch. It really works very well, and consistently gets very good reviews. This is in part because it is quite well written, in fairly formal language with a hint of humor, and remains engaging despite a plot that is frankly simplistic to the point of being inane. The illustrations, despite being just as simplistic, if not more so, do add a unreal visual texture to the story. You are left with the impression of a story so simple that it obviously would have been written by someone, and Wilson wrote it better than anyone else could have. It is also delightfully creepy. I highly recommend it.