Because a "film semi" leaves certain acts to the imagination (or hides them via shadows/angles), the brain must fill in the gaps. For many, what the mind imagines is far more potent than what a camera shows. This tease-and-release mechanism is neurologically similar to foreplay.
Jacques Lacan’s mirror stage and Metz’s imaginary signifier argue that cinema’s deep structure plays on desire, lack, and identification. The camera’s movement mimics the glance; the edit mimics the blink. film semi