Lägg märke till hur lugn hon blir så fort musiken börjar.

Lägg is the imperative form of lägga (to lay / put). In the expression lägga märke till, it means notice or pay attention to.

So Lägg märke till ... means Notice ...

This is a command or instruction, like:

• Titta! = Look!
• Lyssna! = Listen!
• Lägg märke till ... = Notice ...

Yes — this is a fixed expression or idiom.

Word by word, it looks like:

• lägga = put / lay
• märke = mark / sign
• till = to

But together, lägga märke till means to notice.

You should learn it as one unit:

• Jag lägger märke till det. = I notice that.
• Hon lade märke till felet. = She noticed the mistake.

A lot of Swedish expressions work like this: the literal meaning is less important than the full phrase.

Because lägga märke till is a fixed verb phrase, and till belongs to it.

In Swedish, some expressions include a verb plus another word such as a preposition or particle. Here, till is part of the whole expression.

So:

• lägga märke till något = notice something
• Lägg märke till hur ... = Notice how ...

You should not move till away or replace it casually if you want this exact meaning.

Here hur means how.

In this sentence, hur lugn hon blir means how calm she becomes.

It introduces a clause that describes what you should notice:

• Lägg märke till hur lugn hon blir ...
• Notice how calm she becomes ...

So hur is not asking a question here. It is introducing an embedded clause after notice.

Because this is not a direct question. It is an embedded clause.

In a direct question, Swedish often has inversion:

• Hur lugn blir hon? = How calm does she become?

But after expressions like Lägg märke till, you use normal clause order:

• hur lugn hon blir

So the subject hon comes before the verb blir.

This is very common in Swedish:

• Jag vet var han bor. = I know where he lives.
• Ser du vad hon gör? = Do you see what she is doing?

Because lugn agrees with hon.

Here lugn is a predicative adjective after blir (becomes), and its form depends on the subject:

• hon blir lugn = she becomes calm
• han blir lugn = he becomes calm
• det blir lugnt = it becomes calm
• de blir lugna = they become calm

Since hon is a singular common-gender person, the correct form is lugn.

Because blir means becomes / gets, not just is.

The sentence is describing a change of state:

• before the music starts, she is not as calm
• then the music starts
• she becomes calm

So:

• hon är lugn = she is calm
• hon blir lugn = she becomes / gets calm

In this sentence, blir is the natural choice because the calmness appears as a result of the music starting.

Here så fort means as soon as.

So:

• så fort musiken börjar = as soon as the music starts

This is a very common Swedish expression for something happening immediately after something else.

Examples:

• Jag ringer dig så fort jag kommer hem. = I’ll call you as soon as I get home.
• Hon log så fort han kom in. = She smiled as soon as he came in.

Do not translate it literally as so fast here. In this context, it functions as a conjunction meaning as soon as.

Yes. så fort can sometimes literally mean so fast / that fast, depending on context.

For example:

• Hon springer så fort. = She runs so fast.

But in your sentence, så fort musiken börjar, it clearly means as soon as the music starts.

So context tells you which meaning is intended.

Because musiken is the definite form: the music.

• musik = music
• musiken = the music

In this sentence, it refers to a specific music event or piece that both speaker and listener can identify from the situation:

• as soon as the music starts

If you said musik börjar, that would sound incomplete or unnatural here.

Swedish often uses the present tense in clauses like this, just like English does in many similar cases.

• så fort musiken börjar = as soon as the music starts

Even though the starting happens after the instruction notice, Swedish normally still uses the present tense.

This is very natural in time clauses:

• Jag går när filmen börjar. = I’m leaving when the movie starts.
• Ring mig så fort du kommer fram. = Call me as soon as you arrive.

So this is normal Swedish grammar.

No. You do not need att here.

After Lägg märke till, Swedish can go directly into the clause:

• Lägg märke till hur lugn hon blir ...

That is normal.

Swedish does not always use a word corresponding to English that or an infinitive marker in places where English learners might expect one.

The sentence can be divided like this:

• Lägg märke till = imperative expression, Notice
• hur lugn hon blir = embedded clause, how calm she becomes
• så fort musiken börjar = time clause, as soon as the music starts

So the structure is basically:

Notice + what you should notice + when it happens

That makes the whole sentence:

• Lägg märke till
• hur lugn hon blir
• så fort musiken börjar.

The original sentence is already natural, but a learner might also hear similar versions such as:

• Lägg märke till att hon blir lugn så fort musiken börjar.
• Se hur lugn hon blir så fort musiken börjar.

The version with hur focuses nicely on the observed result: how calm she becomes.

The version with att is also possible, but it is slightly different in structure:

• Lägg märke till att ... = Notice that ...
• Lägg märke till hur ... = Notice how ...

So the original sentence is very natural and expressive.

märke is pronounced roughly like MER-keh, with Swedish vowels, not like English mark.

A few useful points:

• ä sounds somewhat like the vowel in English bed, though not exactly
• the r affects the sound in a Swedish way
• the final e is pronounced, unlike in many English words

So märke is two syllables: mär-ke

This is worth practicing because lägga märke till is a very common phrase.

Not very well. A word-for-word translation would sound awkward in English.

A natural translation is:

• Notice how calm she becomes as soon as the music starts.

That is better than trying to map each Swedish word directly.

This sentence is a good example of why it helps to learn:

• fixed expressions: lägga märke till
• clause patterns: hur lugn hon blir
• time expressions: så fort

rather than only individual words.