I think about maybe 5% of the people playing the game, even knew you could find animal crackers in Ep. 3. It is actually part of the trailer, you sort of have to go out of your way when you are investigating the train with Ben. You have to go all the way up tp the front of the train and then find a car with a walker in it and then find a way to kill it. Then you give the animal crackers to Katjaa, it doesn't affect the story in any way though.