Not for nothing was Hollywood in its heyday known as the dream factory. In the movie houses of the period the curtains would open and a succession of gigantic images would emerge from the darkness. Then there would be music—and later sound—and audiences would be encompassed by the film-makers’ dream. Soon movies included their characters’ dreams. Almost certainly this began with The Cabinet of Dr Caligari (1920) where the main action that takes place in marvellously stylised sets turns out to be a dream by one of the protagonists. Later film audiences were being encouraged to recognise different levels of…