He kept practicing answers to potential questions before the interview, like shadowboxing with his thoughts.

shadowboxing 是由 shadow（影子）和 boxing（拳击）组成的复合词，字面意思是"对着影子打拳"，指拳击运动员在没有对手的情况下进行的空击训练。比喻独自练习或准备某事。