His father pulled some strings to get him that internship at the law firm.

pulled 是动词 pull 的过去式。 pull strings 是一个固定短语，不能按字面"拉线绳"来理解，比喻"暗中动用关系或影响力来达到目的"，在句中指父亲靠人脉帮儿子弄到了实习机会。