Blink!
A tenth of a second is all it takes - yes, the blink is a marvel of human physiology that clears dust away from the eye and helps lubricate the eyeball. We have learned to cope with momentary blackout by suppressing those parts of the brain that monitor visual change, in a manner similar to the way we are able to ignore our blindspot caused by the optic nerve entering the eye. So why the hell do I often end up photographing people with their eyes closed?!