Even for a 1950's movie, this Sci Fi was pretty creepy. What makes it so scary is that you are dealing with the unseen rather than the visible. You never see the aliens. Rather, they are invisible and harvest themselves in people, taking over their bodies much like a virus. Plus, the themes of submitting and giving oneself over to the invaders brings to mind the evil of Communism and brainwashing.
Review of Invasion of the Body Snatchers
