There is a scene in the Marx Brothers’ film Duck Soup which never fails to leave a profound impression on the audience. The President of ‘Freedonia’, played by Groucho, is pursuing Harpo who is a foreign agent, and has succeeded in infiltrating the palace disguised as his double. Harpo is cornered beside an open doorway and is about to be captured when he decides to turn his disguise into a new means of escape. He goes into a routine in which he literally plays Groucho’s double, copying every gesture in perfect synchrony to create the optical illusion that the doorway is a mirror, and the President is merely watching his own reflection in it. The silent dance continues for some time with Groucho trying to catch his double out of step, by freezing or making an unpredictable movement, until finally the illusion is shattered when each changes places with the other by stepping through the mirror, at which point the chase begins once more.
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