open (your) mouth
to say something.
Ms. Parker looks fragile, but as soon as she opens her mouth you know she's a tough, no-nonsense woman.
英语词组固定搭配大全包含18674条英汉双解词组，基本涵盖了全部常用英文词组、短语的翻译及用法，是英语学习的有利工具。