Mirror reflects honestly what are in front of it. By itself it is still and no surprise could be expected(except for the Magic Mirror). However, be they together, some interactivity could occur.
Audience is an installation that is consisted of 64 mirrors, conceived by rAndom International. The mirrors would chase someone they find interesting by turning their heads towards them and following them.
Audience from Chris O'Shea on Vimeo.
The video shows how audience noticed, tried, played around with and even danced in front of the mirrors.
There is another mirror installation that was in my mind. Aleph is an outdoor display built from thousands of kinetic mirrors. (http://www.aether.hu/aleph/) Each mirror reflects part of the space, but a matrix of small mirrors can by together show other images by adjusting their inclinations. The computer analyzes the surroundings by using cameras, and then give the information to a network of microcontrollers to position the mirrors.
The designer who created the Aleph says, “(The computer is) easy to create seductive content, but it is hard to make it multi-sensual, there is an embedded distancing in this medium.” Here, the mirrors together become a new kind of user interface to create interesting experiences for audience. Simple as mirror, the installations change how people look at the ordinary things in life and their behaviors.
Another installation that play with mirrors: http://www.smoothware.com/danny/brokenmirror.html