"Open your mouth" is the Engpsh equivalent of "请张开嘴巴" in Chinese.
This phrase is often used as a request for someone to open their mouth, either for speaking or for medical examination purposes.
Examples in Engpsh:
"Open your mouth and say 'ah'" (request for a medical examination of the throat)
"Open your mouth and let's hear what you have to say" (request for someone to speak their thoughts or opinions)
中文翻译：
"张开嘴巴说'啊'"（医疗检查喉咙的请求）
"张开嘴巴让我们听听你的想法"（请求某人说出他们的想法或见解）