What the Butler Saw was the title of a very popular Mutoscope reel. (Mutoscopes were coin-in-the-slot devices by which an individual could view a short motion picture). What the butler saw, presumably through a keyhole, was a woman partially disrobing. Machines presenting this reel were so ubiquitous that, in England, mutoscopes are known as What-the-butler-saw machines.
The phrase became a byword or idiom for shameful secrets or voyeurism and was used in this sense as the title of other works:
What the Butler Saw: 250 Years of the Servant Problem is a 1962 book by E. S. Turner.
What the Butler Saw is the title of an episode of the television comic drama The Avengers. The episode premiered February 25, 1966 in the UK and July 28, 1966 in the United States. US Premiere (New York, Season 1): 28 July 1966.
What the Butler Saw is the title of a 1969 play by Joe Orton which the Sunday Telegraph called "a comedy classic of English Literature."
What the Butler Saw is the title of a 1980 recording by the musical group Squeeze.
What the Butler Saw: A 3-D Saucy Bedroom Romp is the title of a 1995 book by Amy Carroll.
What the Butler Saw: Selected Writings is the title of a book of writings by Stuart Morgan published in 1996.
Where Queen Elizabeth Slept and What the Butler Saw: A Treasury of Historical Terms from the Sixteenth Century to the Present is the title of a 1998 book by David N. Durant.
