"I'm not actually sure if guilt is an emotion. In fact, that was - at the very beginning of this process, we realized, man, we really don't know very much about the subject. So, we better do some research, and we started looking around online. We found some scientists think that there are basically three emotions. Others went up to 27. Others had 16. Some were in the middle. So, we were kind of left with no definitive answer to our basic question - how many are there? Dr. Paul Ekman, who worked in San Francisco - still does - which is where Pixar Animation Studios is - he had, early in his career, identified six. That felt like a nice, manageable number of guys to design and write for. It was anger, fear, sadness, disgust, joy and surprise. And as I was sort of doodling, I was thinking, surprise and fear - probably fairly similar, so let's just lose surprise. And that left us with five."