When Jesus healed a blind man, all the guy had to do was put mud over his eyes, wash it out, and he could see. Simple as that. But apparently it's not as simple as that. The New Yorker has posted an old Oliver Sacks article about a man whose sight was restored after fifty years of blindness. It turns out that he was extremely confused—at first he didn't even realize that he was seeing—and had a hard time, for instance, distinguishing shapes and colors, because he had never done it before. This part is especially remarkable—when they take the man, Virgil, to the zoo:

In general, it seemed to us, if Virgil could identify an animal it would be either by its motion or by virtue of a single feature—thus, he might identify a kangaroo because it leaped, a giraffe by its height, or a zebra by its stripes—but he could not form any over-all impression of the animal. It was also necessary that the animal be sharply defined against a background; he could not identify the elephants, despite their trunks, because they were at a considerable distance and stood against a slate-colored background.

Finally, we went to the great-ape enclosure; Virgil was curious to see the gorilla. He could not see it at all when it was half hidden among some trees, and when it finally came into the open he thought that, though it moved differently, it looked just like a large man. Fortunately, there was a life-size bronze statue of a gorilla in the enclosure, and we told Virgil, who had been longing to touch all the animals, that he could, if nothing else, at least examine the statue.

Exploring it swiftly and minutely with his hands, he had an air of assurance that he had never shown when examining anything by sight. It came to me—perhaps it came to all of us at this moment—how skillful and self-sufficient he had been as a blind man, how naturally and easily he had experienced his world with his hands, and how much we were now, so to speak, pushing him against the grain: demanding that he renounce all that came easily to him, that he sense the world in a way incredibly difficult for him, and alien.

His face seemed to light up with comprehension as he felt the statue. “It’s not like a man at all,” he murmured. The statue examined, he opened his eyes, and turned around to the real gorilla standing before him in the enclosure. And now, in a way that would have been impossible before, he described the ape’s posture, the way the knuckles touched the ground, the little bandy legs, the great canines, the huge ridge on the head, pointing to each feature as he did so.

It ends up being a bit of a sad and depressing story in the end, but it's very much worth reading. The idea that perception involves much more than simply letting a bit of light hit your eye isn't, I gather, terribly groundbreaking, but Virgil's case illustrates it quite nicely.