I ran into the same friend two days in a row on the street. It’s interesting how you have a physiological reaction to seeing someone familiar – the ‘flashbulb of recognition’- a split-second before you even realize what you’re reacting to. It’s a bit like the way birds seem to move in an absolutely instantaneous way without any time for forethought or conscious processing.
What’s amazing is how good the brain is at remembering faces. Someone whom we haven’t seen for years is instantly recognized (before we even realize we’ve recognized them) on account of millimeter distinctions in facial structure. Imagine if it were not this way and we had to fumble around in order to recognize somebody we hadn’t seen for an hour or so. I suppose it would be socially acceptable to peer confusedly at, or even grope with our fingers, the facial features of people we know well, depending on the situation.