The film parodies the medium of animation itself by referencing the Thaumotrope (optical toy depicting a bird and a cage on opposite sides of a disc which combine together when spun). This iconic image has come to epitomise the illusion of moving image in its simplest form. Normally moving image hides its underlying illusion and creates a seamless flow. Here this is turned on its head and the mechanics of the illusion become an integral part of the film.
Sound and image are combined with precision. The use of images is economic (mainly four). The creation of surprise and suspense, more famously associated with the film maker Alfred Hitchcock is mastered. Watch it full screen, high volume and only once.