One thing I'll never quite be able to comprehend is how come I can be standing looking at a stretch of water that's a foot deep and as clear as drinking water and not see a fish? Now, I can see every rock, pebble, and piece of stuff floating in the water, but not see a single fish. Then, when my fly is drifting through the run, wham, a fish hits it.
These guys are great at camouflage. It's amazing.