Taking faces for granted

Some people suffer from prosopagnosia - or face blindness - which affects about 2% of the population.

Prosopagnosiacs can't identify people from their faces. They will carefully scan faces for details like moles, skew teeth and monobrows. When they view a face from an odd angle, they might as well look at a new face. The rest of us process faces so quickly that we have stopped noticing them.