The Fly (1986)

Seth Brundle, a brilliant but eccentric scientist attempts to woo investigative journalist Veronica Quaife by offering her a scoop on his latest research in the field of matter transportation, which against all the expectations of the scientific establishment have proved successful. Up to a point. Brundle thinks he has ironed out the last problem when he successfully transports a living creature, but when he attempts to teleport himself a fly enters one of the transmission booths, and Brundle finds he is a changed man. This Science-Gone-Mad film is the source of the quotable quote "Be afraid. Be very afraid."