In section 3 of the final chapter of Impro (titled "Masks and Trance") author Keith Johnstone explains the strange power of some simple masks:

Masks seem exotic when you first learn about them, but to my mind Mask acting is no stranger than any other kind: no more weird than the fact that an actor can blush when his character is embarrassed, or turn white with fear, or that a cold will stop for the duration of the performance, and then start streaming again as soon as the curtain falls ... Actors can be possessed by the character they play just as they can be possessed by Masks. ... We find the Mask strange because we don't understand how irrational our responses to the face are anyway, and we don't realise that most of our lives is spent in some form of trance, i.e. absorbed. What we assume to be 'normal consciousness' is comparatively rare ... A Mask is a device for driving the personality out of the body and allowing a spirit to take possession of it.

^z - 2013-01-30