As an example, in ''Monsters an company'', Boo gives a clown fish (Nemo) to Sully the monster. In the next movie, the main character in Nemo is the clown fish. Moreover, in Nemo, the dentist has a comic book titled" The Incredibles."
In "The Incredibles", the opening scene shows a villain who is dressed like a street mime. In "Ratatouille", we see the street mime from the Incredibles, and in a scene where the rat is running away, we see the shadow of Doug the dog.