U ambulanti smo morali čekati, jer je jedna druga mačka glasno mijaukala iza vrata.

Ambulanti is in the locative singular.

The noun is ambulanta. After u when it means in / inside / at a place, Croatian normally uses the locative:

• u ambulanti = in the clinic / at the clinic

Compare that with u + accusative, which is used for motion into somewhere:

• Idem u ambulantu. = I’m going into the clinic.
• U ambulanti smo čekali. = We were waiting in the clinic.

So here it is locative because the sentence describes location, not movement.

This is about Croatian clitic placement.

The word smo is a clitic (a short unstressed form), and clitics usually go in the second position of the clause.

In this sentence, the first unit is U ambulanti, so smo comes right after it:

• U ambulanti smo morali čekati.

That is very natural Croatian word order.

You can also say:

• Morali smo čekati u ambulanti.

That is also correct, but the focus is slightly different. The original sentence puts u ambulanti first, probably to set the scene.

Morali agrees with the implied subject we.

The verb phrase is:

• smo morali čekati = we had to wait

The form morali is the past active participle plural masculine/mixed form of morati.

In Croatian past tense, this participle agrees with the subject:

• mi smo morali = we had to, if the group is masculine or mixed
• mi smo morale = we had to, if the group is entirely female

So morali tells you the speaker is either:

• male, speaking with others, or
• part of a mixed-gender group

Because morati is a modal verb, and modal verbs are followed by an infinitive.

So:

• morati čekati = to have to wait
• morali smo čekati = we had to wait

This works much like English:

• We had to wait.

Other common Croatian modal patterns are similar:

• mogu doći = I can come
• želim spavati = I want to sleep
• moramo ići = we have to go

Jedna druga mačka means another cat or a different cat.

Here:

• jedna can function a bit like a / one
• druga means other / different / another

So together they emphasize that it was some other cat, not the one already being talked about.

Croatian often does this kind of thing where English would simply say another.

You may also hear just:

• druga mačka

But jedna druga mačka sounds very natural when the speaker means some other cat.

Here it means other / another, not second.

The adjective drugi / druga / drugo can mean either:

• second
• other / another

Context tells you which meaning is intended.

In this sentence, jedna druga mačka clearly means another cat. The sentence is not counting cats.

Again, this is clitic placement.

The word je is a clitic, just like smo, so it tends to appear very early in the clause.

After jer, it is normal to say:

• jer je jedna druga mačka glasno mijaukala...

That sounds natural and standard.

A version like:

• jer jedna druga mačka je...

is much less natural in ordinary Croatian.

So the important idea is: short auxiliary forms like je, smo, sam, su usually do not stay where English would put is / are / was. They follow Croatian clitic rules instead.

Mijaukala is the feminine singular past participle of the verb mijaukati = to meow.

It agrees with the subject:

• mačka is a feminine singular noun
• so the verb form is mijaukala

Compare:

• mačka je mijaukala = the cat meowed
• pas je lajao = the dog barked
• dijete je plakalo = the child cried

So the ending helps show grammatical gender and number.

Glasno is an adverb, meaning loudly.

It comes from the adjective glasan = loud.

So:

• glasna mačka = a loud cat
• glasno mijaukati = to meow loudly

In the sentence:

• glasno mijaukala = was meowing loudly

This is very similar to English adjective/adverb pairs:

• loud → loudly

Here iza means behind, and in this meaning it takes the genitive:

• iza vrata = behind the door

So vrata here is in the genitive form.

A useful thing to remember is that many Croatian prepositions require specific cases, and some prepositions can take different cases with different meanings.

With iza, you will commonly see:

• iza kuće = behind the house
• iza vrata = behind the door

Because vrata is a plural-only noun in Croatian. This is called pluralia tantum.

Even when referring to a single door, Croatian normally uses the plural form:

• vrata = door / doors, depending on context

So:

• iza vrata = behind the door
• otvori vrata = open the door

This is one of those vocabulary items you simply have to learn as a special noun.

Other languages do similar things with certain nouns, so it may feel strange at first, but it is completely normal in Croatian.

Because jer introduces a subordinate clause meaning because, and in standard Croatian this clause is separated by a comma.

So:

• U ambulanti smo morali čekati, jer je jedna druga mačka...

This is standard punctuation.

English sometimes handles commas around because differently, but in Croatian the comma before jer is normal and expected.

Yes, often you can.

For example:

• U ambulanti smo morali čekati, jer je jedna druga mačka glasno mijaukala iza vrata.
• U ambulanti smo morali čekati zato što je jedna druga mačka glasno mijaukala iza vrata.

Both mean roughly the same thing.

A small difference:

• jer is very common and compact
• zato što can sound a bit more explicit or heavier

In everyday speech, both are normal.

Yes. Croatian word order is more flexible than English, although not completely free.

Possible versions include:

• U ambulanti smo morali čekati, jer je jedna druga mačka glasno mijaukala iza vrata.
• Morali smo čekati u ambulanti, jer je jedna druga mačka glasno mijaukala iza vrata.

Both are correct. The difference is mostly about focus and style.

The original version starts with U ambulanti, which sets the location first. That is a very natural way to begin a sentence when you want to establish the scene.