what the butler saw

noun[before a noun]2

1. •
   (UK) A mutoscope; an amusement machine that shows a sequence of images or animation, often of a titillating nature, viewed via a peephole

   • the fairground – women wanting to read your palm, a what-the-butler-saw, the waxworks, the dodgems, ghost train, tunnel of love... — 2013
2. •
   (UK, slang) A story or film of titillating activity observed by voyeurism.

   • In Last Tango, we encounter another cast of off-the-wall characters (does Wales really have this many eccentrics?) as Louie becomes involved in Aberystwyth's 'What the Butler Saw' film industry. — 2016