One of the coolest things we covered a few weeks ago in my Video Construction class lecture was some cinematic fun using optical illusions like the Ames Room. This still freaks me out that my brain is so easily and completely fooled.
Here is a clip from the BBC doco Brain Story which shows the 'magic' in action:
See also: Ames Room and check out more on youtube. There is lots about visualisation that is about delivering a vision for people and using tools like this is just plain clever. The LotR films used this for the Hobbits and lots of CG is about creating what our minds expect to see or using that to our advantage.