The document contrasts informal and formal language through examples of Julie interacting with her friend Nat and a teacher. [1] Informal language examples show Nat and Julie laughing together after burping loudly and making jokes about it. [2] Formal language examples depict Julie accidentally burping in front of her teacher, feeling embarrassed, and properly excusing herself. [3] Differences highlighted include more casual greetings, responses, and actions in informal settings versus more polite and respectful language when formal.