@bythewell - Another, probably better example, is the alternate Gollum in Lord of the Rings. Whenever Gollum is feeling conflicted, he begins to talk to himself and the camera makes it look as though there are two of him, each talking to the other. One is the selfish, cunning, corrupted side of Gollum and the other is the side that wants to be a better person.
It's a bit awkward at first, but it's a powerful tool for storytellers as the symbolism of choices is something that we can all relate to. We might not consciously have an internal doppelganger, but it's a rare person who isn't of "two minds" when it comes to certain issues.