If the eye can detect a single photon, it must mean that the triggering system in the human eye, which starts the electrical signal that carries the visual information to the brain, needs less energy than a photon contains to be triggered. That's pretty amazing to me.

How many photons does a CCD chip need to change one pixel from pitch black? A billion? 1e20? I'm curious to know.

If we could figure out how this triggering system works, we could build amazing stuff. Probably more than really good camera chips.