We were conflicted about this Tough-o-Meter. On the one hand, O'Connor's language isn't hard, exactly. Check out this sentence:
She was almost ready to go, standing before the hall mirror, putting on
her hat, while he, his hands behind him, appeared pinned to the door
frame, waiting like Saint Sebastian for the arrows to begin piercing him. (2)
No SAT words here: pretty straightforward diction. But look at that sentence structure—clause after clause, building up information from matter-of-fact ("She was almost ready to go") to allusive and literary (Saint Sebastian).
To get the most out of this sentence, you'll need to know that Saint Sebastian was arrowed to death for being Christian. And that ludicrous comparison—this guy about to ride a bus with his mom feels like an executed martyr—clues you into O'Connor's highly complex, literary, and (dare we say) challenging theme.