Once Upon a Monster was one of Cookie's favorite interactive books! He used to spend hours and hours exploring its pages, meeting all sorts of monsters, making friends with them, helping them solve their problems, and generally making the world a better place. One day, Cookie was reading the book when he smelled the most delicious smell in the world - freshly baked chocolate chip cookies. In his hurry to eat all of the delicious cookies, he hastily dropped the book. When he went to look for it again, he couldn't find it. He searched and searched, but the book was gone. So, when Elmo brought Once Upon a Monster to Cookie Monster, he was delighted!