Research had played a key role in previous Pixar films; the creative team had toured toy stores for Toy Story and crawled around with insects for A Bug’s Life. But monsters did not lend themselves to scrutiny. A trip to the public library was largely unproductive.

Interviews with kids revealed that while they believed in monsters, they were hazy on the details. The filmmakers finally decided to unleash artists and illustrators to create monsters from their own imagination. “Given the choice between serious study and making it up….we decided to just make it up,” says Pete Docter.