Wallach touched my arm. "You're making the standard, erroneous assumption that a sense of perception will give its owner a blueprint-clear grasp of the mechanical details of some machinery. It doesn't. Perception, as I understand it, is not even similar to eyesight."
"But—" I fumbled on—"surely there must be some common reference there, even granting that perception isn't eyesight. So how does perception work?"
"Tom, if you were blind from birth, I could tell you that I have eyesight that permits me to see the details of things that you can determine only by feeling them. This you might understand basically. But you could never be made to understand the true definition of the word 'picture' nor grasp the mental impression that is generated by eyesight."
"Well," I persisted, "can he penetrate flesh?"
"Flesh?"
"Holly's heart has stopped," I said. "But it hasn't been removed. If Harla can perceive through human flesh, he might be able to perceive the large, single organ in the chest cavity near the spine."
Teresa said, "Harla's perception gives him a blurry, incomplete impression." She looked at me. "It is something like a badly out-of-focus, grossly under-exposed x-ray solid."
"X-ray solid?" I asked.
"It's the closest thing that you might be able to understand," she said lamely.
I dropped it right there. Teresa had probably been groping in the dark for some simile that would convey the nearest possible impression. I felt that this was going to be the nearest that I would ever get to understanding the sense of perception.