Have you ever tried to point something out to your cat, like a spider that desperately needs killing, and the cat acts like he/she can't see a thing? I've also pointed out interesting things in the backyard, like squirrels and chipmunks, and he just stares blankly past them (this is through the window, of course - no chance of him actually getting the rodents). Then there was the time that I had him outside on his leash and harness (which he tolerates only to get some fresh air), and he was so busy waiting for a particular chipmunk to emerge from a hole in the tree, that he didn't see a mouse that ran literally past his nose, about 3 inches in front of him.