As a child, Pete Docter, director of Monsters Inc., I knew I had horrible monsters hiding in your closet waiting to leave. Years later, inspired by this fact to tell the story of these monsters, playing with the idea that that was his job. 
The story was very elaborate, so that parallel plot lines are created for each character and also for scenarios where everything goes. Buildings of Monstropolis were designed taking into account the physical needs of each monster that lived, so each house has different forms and each one is tailored to the needs of each monster depending on their shape, size and number of tentacles.
Each character was carefully designed in appearance and personality. In an original storyline, Sully was a failure at work and everyone was laughing at him, and the age of Boo had many changes. A personality like Boo is not easy to develop, especially when your vocabulary does not exceed 3 words, so that your screen performance had to be very expressive for the ability to convey their feelings.
technical side also was a big challenge ... 2,320,413 animated moving hairs on the skin of Sully, and their movement depends on the creation and modification of programs used in 3D animation, including Render Man DSO (Dynamically Shared Object), a program that distributes the hair on character, reads data from the simulator and run an application that contains information about each of the hairs (length, color and other features).
