In a classic bit of foolery from the 1930s film comedy Duck Soup, Harpo Marx becomes the mirror image of Groucho, right down to the greasepaint moustache, closely mimicking his brother's every gesture and grimace as they face each other through an open doorway. Each is dressed in an identical nightshirt and nightcap. Their movements are carefully synchronized as they frolic on either side of the threshold. And then, this being a Marx Brothers movie, an anarchic impulse swiftly takes hold. Groucho ends an impromptu dance routine with a pirouette, while Harpo remains standing, imitating only the final flourish. Groucho apparently fails to notice that his mirror image is cutting corners. He briefly disappears from view, returning with a white Panama hat held behind his back. Simultaneously, Harpo reappears on his side of the door frame, and we see he is holding a black top hat behind his back. Each turns to face the other once again. Groucho leans forward, carefully scrutinizing his double, then steps across the threshold as Harpo circles around. As they change places, Groucho spots the black hat Harpo is holding behind his back. They circle around once again, and Groucho triumphantly places the white hat on his head, just as Harpo by slight of hand places an identical hat on his head. And so it goes, until Chico suddenly appears in the doorway dressed in a nightshirt and nightcap with a greasepaint moustache of his own.
This routine works by briefly creating the illusion that Groucho is seeing his own reflection in a full-length mirror and then by undermining it. It's funny on film, but I suspect we would find it profoundly unsettling if our mirror image suddenly developed moves of its own. The ability to recognize one's own image in a mirror is regarded as a key measure of self-awareness. Only a handful of other species have demonstrated mirror self-recognition, and even humans must acquire this ability as part of their normal cognitive development. Autistic children and others with severe cognitive impairments may never make a connection between themselves and the image they see in the mirror.
To what extent is our sense of self dependent on seeing ourselves reflected in the world? What if there were no mirrors or other external images to go by, and we had no way to picture the face we present to others? Absent such a reminder, we can put a face to just about everybody we meet except for the one person we are most intimately acquainted with. Our face is worn like a mask that can't be removed and, as seen from the inside, it is quite invisible to us. Douglas Harding reminds us that what can actually be seen from our vantage point is a body that extends from the shoulders down but doesn't appear to be connected to anything above. What we actually see is nothing at all -- or everything, depending on whether we are focused on ourselves or on the world beyond. This provides an essential clue as to what we should looking for in life: not a mirror but a window.
Douglas Harding, On Having No Head