The exception to the parole proof rule is that where the meaning of words used in the contract is ambiguous or uncertain, prior negotiations will be taken into account for reference. Particularly, when the term is based on a specific request and an important topic, a negotiation or statement can help interpret the term. Jimmy raised a question regarding the statement regarding customer service, and Claudia cleared Jimmy's doubts and said she just wanted Jimmy to help her. Additionally, the statement regarding customer service may be considered a collateral oral contract to assist the written contract. During the negotiation, Jimmy pointed out that he was bad at serving customers and was unwilling to do so. The statement is therefore a promise and without other influencing factors. Furthermore, according to Jimmy's intention, no obligation to serve customers is the premise for acceptance of the offer. Even when Claudia promised to pay double, Jimmy is still reluctant to serve customers, showing that customer service should not be included in other related activities.