What the Butler Saw is a mutoscope reel, and an early example of erotic films dating from the early 1900s. It depicted a scene of a woman partially undressing in her bedroom, as if some voyeuristic "butler" were watching her through a keyhole. The film was seen by depositing a coin in a freestanding viewing machine, which then freed a hand-crank on the side which was turned by the viewer. Social standards are subject to change, and by the 1950s this and similar films were considered harmless when compared to contemporary erotica.
The title of this feature became widely used in Britain as a generic term for devices and movies of this kind. The phrase had entered British popular culture after the 1886 divorce case of Lord Colin Campbell and Gertrude Elizabeth Blood. The trial hinged on whether their butler could have seen Lady Campbell in flagrante with Captain Shaw of the Metropolitan Fire Brigade, through the keyhole of their dining room at 79 Cadogan Place, London.
- Katherine Mullin (2003). James Joyce, sexuality and social purity. Cambridge University Press. p. 145. ISBN 0-521-82751-5.
- Paul Clee (2005). Before Hollywood: from shadow play to the silver screen. Houghton Mifflin Harcourt. p. 133. ISBN 0-618-44533-1.
- Roger Wilkes (7 April 2001). "Inside story: 79 Cadogan Place". The Daily Telegraph. Archived from the original on 19 May 2010.