Computers
The city's central computer told you?! R2D2, you know better than to trust a strange computer!
C3P0
When I teach math to students who want to use calculators or argue with people who like voting by touchscreen, I always find myself trying to explain why you should be careful trusting machines too much. Even though they make very few mistakes of their own, human error/corruption is always present. I just remembered the best, simple demonstration of this principle: