In Monsters, Inc. they get power from children’s screams after they get scared by monsters. However, there was an accident and a little girl came into the monster’s world, where Mike and Sully were trying to hide her. Well, not everything went according to plan and she ended up screaming and crying after Mike takes a teddy bear from her.
When Mike takes the teddy bear the first time, there was a picture on the wall behind the desk. However, later when Sully gives the bear back, the picture is gone.