Doodlebug (1997) - Christopher Nolan's First Film (1997)

This psychological short-film has gained cult following, especially given the heights which Nolan's now climbed since making it.
The film concerns a grungy man, in a filthy apartment. He is anxious and paranoid, trying to kill a small bug-like creature that is scurrying on the floor. It is revealed that the bug resembles a miniature version of himself. He squashes the bug with his shoe. However, every movement the "doodlebug" makes is later matched by the man himself, and he is later squashed by a larger version of himself.