One night they went out on another bender, and once again, Flannery refused to come, and they left her on the porch. And there was a tremendous thunder and lightning storm and [when they went back] there was Flannery kneeling on the porch. And Pat said: “What are you doing?” And Flannery said, “Look, can’t you see it?” And she’s pointing to some knot in the porch wood. And then she said: “Jesus’ face.” And Pat said to me, “That happened. And ever since then, I’ve not liked that woman.”
Just today, though, I had this thought: Assuming that this incident truly occurred, could O'Connor have done this as a private joke on Highsmith, a way of playing off of Highsmith's preconceptions and judgments of the devout, abstemious (yet also wickedly humorous) O'Connor?
Maybe, maybe not. But it does seem like the type of thing that one of O'Connor's characters would do.