Mở miệng.

Mở means to open, and miệng means mouth.

So the phrase is literally open mouth.

Vietnamese often leaves out the subject when it is obvious from context, especially in commands.

So Mở miệng. naturally means Open your mouth. Even though you is not said, it is understood.

Yes. It is a perfectly normal short imperative sentence.

Vietnamese commands are often just:

• verb + object
• or even just the verb

So Mở miệng. is complete and natural.

Yes. Miệng is the everyday word for mouth.

It can refer to:

• the physical mouth
• speech, in some expressions
• the opening of something, in certain contexts

In this sentence, it simply means the body part.

You can say mở cái miệng, but it changes the tone.

• Mở miệng = neutral, direct command
• Mở cái miệng = more emphatic, and sometimes rough, impatient, or scolding depending on tone

The classifier cái is often omitted when talking about body parts in simple instructions.

A rough guide is:

• mở ≈ muh with a dipping-rising tone
• miệng ≈ something like mee-ung with a heavy, cut-off tone

A few pronunciation notes:

• ơ in mở is not the same as English o
• miệng ends with -ng
• both words have tones, which are essential in Vietnamese

If you want to sound natural, the tones matter just as much as the consonants and vowels.

• mở has the hỏi tone
• miệng has the nặng tone

These tones are very important. If you change the tone, you may produce a different word or make yourself hard to understand.

By itself, it is a direct command. It is not automatically rude, but it is quite blunt.

Whether it sounds fine or rude depends on context:

• normal from a doctor or dentist
• fine in urgent instruction
• possibly too direct in everyday polite conversation

To make it softer, Vietnamese often adds polite words or pronouns.

You can soften it by adding particles or pronouns, depending on who you are talking to.

Examples:

• Mở miệng ra. = Open your mouth.
• Há miệng ra. = Open your mouth wide.
• Mở miệng ra nhé. = Open your mouth, okay?
• Em mở miệng ra nhé. = Open your mouth, okay? (to someone younger or in an appropriate pronoun relationship)
• Xin mở miệng. = Please open your mouth. (grammatically possible, but less common in everyday speech)

In real life, tone of voice is very important for politeness.

Both can relate to opening the mouth, but they are not exactly the same.

• mở miệng = open the mouth
• há miệng = open the mouth wide

In a medical or dental situation, há miệng ra is extremely common because the person is usually being asked to open wide.

Ra often adds a sense of outward opening or completion.

So:

• Mở miệng = open your mouth
• Mở miệng ra = open your mouth up / open your mouth out

In many situations, ra makes the instruction sound more natural and complete, especially in speech.

Yes, in some contexts mở miệng can be used figuratively to mean to open one’s mouth, especially to begin to say something.

For example, in a longer sentence it might suggest:

• speaking up
• starting to say something
• daring to say something

But as a short command Mở miệng., the most likely meaning is the literal one: Open your mouth.

Not always. Other very common possibilities are:

• Há miệng ra. = Open your mouth wide.
• Mở miệng ra. = Open your mouth.
• Há miệng to ra. = Open your mouth wide.
• Mời anh/chị mở miệng. = Please open your mouth. (more polite/formal)

So Mở miệng. is correct, but it is just one of several natural options.

Usually not, unless needed for clarity or emphasis.

English says Open your mouth, but Vietnamese often just says Mở miệng because it is obvious whose mouth is meant.

If necessary, Vietnamese can specify:

• mở miệng em
• mở miệng ra
• mở miệng của bạn

But in a simple command, that would usually be unnecessary.

The period simply shows it as a written sentence. In speech, what really matters is intonation and context.

Without special intonation, Mở miệng. sounds like a straightforward command. If spoken gently, it can sound caring; if spoken sharply, it can sound strict.