Brinem o psu, a pas laje kada se izgubi.

Because the preposition o normally requires the locative case when it means about / concerning.

• basic form: pas = dog
• locative singular: psu

So:

• o psu = about the dog

This is very common in Serbian: a preposition changes the form of the noun that follows it.

Examples:

• pričam o gradu = I am talking about the city
• mislim o tebi = I am thinking about you
• brinem o psu = I care about / worry about the dog

Yes, pas is a somewhat irregular noun.

Its nominative singular is:

• pas = dog

But in other cases, the stem changes:

• psa (genitive/accusative)
• psu (dative/locative)
• psom (instrumental)

So the vowel a disappears in some forms. This happens with a number of Serbian nouns.

Useful singular forms of pas:

• pas = dog
• psa
• psu
• psa
• pse
• psu
• psom

So o psu is simply the correct locative form.

Brinem is the 1st person singular present form of brinuti.

So:

• brinem = I worry / I care

In this sentence, brinuti o + locative means something like:

• to care for
• to look after
• to be concerned about

Depending on context, brinem o psu can sound like:

• I care for the dog
• I look after the dog
• I worry about the dog

Serbian brinuti often covers both emotional concern and taking care of someone/something.

A often means something like and, but it is not exactly the same as English and in every situation.

In Serbian, a often connects two clauses by showing a contrast, switch of topic, or simply a parallel statement.

Here:

• Brinem o psu, a pas laje...

This can feel like:

• I care for the dog, and the dog barks...
• I care for the dog, while the dog barks...
• I care for the dog, but the dog barks...

The exact nuance depends on context. In many beginner translations, a is best understood as and, but it often has a slight contrastive flavor.

Compare:

• i = and, simple addition
• a = and / while / but, with some contrast or shift

Because in the second clause, pas is the subject of the verb laje.

Subjects normally go in the nominative case, and the nominative singular is:

• pas

So:

• o psu = about the dog / for the dog → after a preposition, so locative
• pas laje = the dog barks → subject, so nominative

This is a very important Serbian pattern: the same noun changes form depending on its role in the sentence.

Laje is the 3rd person singular present of lajati = to bark.

So:

• ja lajem = I bark
• ti laješ = you bark
• on/ona/ono laje = he/she/it barks

Here:

• pas laje = the dog barks

The sentence uses the present tense to describe something habitual or generally true.

Serbian often uses the present tense for habitual, repeated, or general actions, just like English.

So:

• Brinem o psu = I care for / look after the dog
• pas laje kada se izgubi = the dog barks when it gets lost

This does not have to mean it is happening right now at this exact moment. It can mean this is what usually happens.

So the present tense here is very natural.

Yes.

• kada = when
• kad = when

They mean the same thing. Kada is a bit more formal or full, while kad is very common in everyday speech.

So both are possible:

• pas laje kada se izgubi
• pas laje kad se izgubi

Both are correct.

This is a very common learner question.

The verb here is izgubiti se, which means:

• to get lost

Without se, izgubiti usually means:

• to lose something

Compare:

• Izgubio sam ključ. = I lost the key.
• Izgubio sam se. = I got lost.

So se changes the meaning a lot here.

In kada se izgubi, the meaning is:

• when it gets lost
• when it loses its way

This is one of many Serbian verbs that are normally learned with se as part of the verb.

Yes, izgubi is present tense: 3rd person singular present of izgubiti se.

The verb izgubiti is a perfective verb, and its present-tense forms are often used in subordinate clauses like this one, especially after words such as kad/kada.

So:

• kada se izgubi = when it gets lost

This is normal Serbian usage.

A useful contrast is:

• gubiti se = to be getting lost / to lose one’s way repeatedly or in an ongoing sense
• izgubiti se = to get lost, to become lost

Here the perfective verb fits well because it refers to the moment or event of becoming lost.

Yes, Serbian word order is fairly flexible.

The given sentence is natural:

• Brinem o psu, a pas laje kada se izgubi.

But other orders are possible, depending on emphasis. For example:

• O psu brinem, a pas laje kada se izgubi.

This puts more emphasis on o psu.

However, for a learner, the original order is a good neutral choice:

• verb first in the first clause
• subject first in the second clause

So yes, word order can change, but the original sentence is perfectly normal.

Yes, there can be a difference.

• brinuti o + locative usually means to take care of / care for
• brinuti za + accusative often means to worry about / be anxious about

So:

• Brinem o psu. = I care for the dog / I look after the dog.
• Brinem za psa. = I’m worried about the dog.

In real usage, the meanings can overlap, but this distinction is useful and common.

So in your sentence, brinem o psu leans more toward caring for / looking after the dog.

Repeating pas is natural and clear here:

• Brinem o psu, a pas laje kada se izgubi.

You generally keep the subject if you want the sentence to sound complete and easy to follow.

If you removed it:

• Brinem o psu, a laje kada se izgubi.

that would sound less natural on its own, because the second clause would be missing an explicit subject. Serbian can omit subjects in many cases, but here repeating pas is the clearest option.

So the repetition is normal, not awkward.