Mirrors are often used as a tool to reflect upon the self. They refract a different image of ourselves, of an ideal or pensive self. Sometimes mirrors are used to start a reflection on acting and taking on a different role. Think about Hamlet. Or Anna Magnani in Bellissima. There are loads of examples in theatre and film , worth looking at, and even visual arts and paintings that interrogate this idea and asks us to take part in this reflection. Would be good to look at some of the philosophical implications and theories too.
I think Black Swan would be a great example to look at through the lens of Freud's notion of a "doppelganger" or "the double" and the way the film uses mirrors to reflect it. – CriticalOtaku7 years ago