张开他的嘴用英语怎么说

"Open his mouth" 意思是张开他的嘴。这是一个常用的短语，用来描述某人将嘴巴张开的动作。

例句:

Open your mouth and say "ah." (张开你的嘴巴说"啊")
The doctor told the patient to open his mouth and stick out his tongue. (医生告诉病人张开嘴巴并伸出舌头)
I had to force the dog to open his mouth so I could check his teeth. (我不得不强迫那只狗张开嘴巴，才能检查他的牙齿)

来源: 这个短语来源于英语中对于“张开”的描述，使用了动词“open”, 和名词“mouth”。