Djevojčica kaže da je zec brži od mačke.

Because je is a clitic in Croatian. Clitics are short, unstressed words that usually go in the second position of their clause.

So in the clause da je zec brži od mačke:

• da = the first element
• je = the clitic, so it comes right after that
• zec = the subject

That is why Croatian prefers:

• da je zec brži od mačke

rather than:

• da zec je brži od mačke ❌

This is a very common Croatian word-order pattern.

Here da means that and introduces a subordinate clause.

So:

• Djevojčica kaže = The girl says
• da je zec brži od mačke = that the rabbit is faster than the cat

Croatian often uses da where English uses that.

Here je is the 3rd person singular present form of biti (to be), so it means is.

In this sentence, it links the subject zec with the adjective brži:

• zec je brži = the rabbit is faster

So yes, in this sentence je is basically is.

Because zec is the subject of the clause da je zec brži od mačke, so it stays in the nominative case.

Croatian usually uses the nominative for the subject of a sentence or clause.

So:

• zec = nominative singular, rabbit / hare
• it is the one that is faster

Brži is the comparative form of brz (fast).

So:

• brz = fast
• brži = faster

This is not formed the same way English adds -er, but it serves the same function.

Examples:

• brz auto = a fast car
• auto je brži = the car is faster

In your sentence:

• zec je brži od mačke = the rabbit is faster than the cat

Croatian commonly forms comparisons with:

• comparative adjective + od + genitive

So:

• brži od mačke = faster than the cat

Here:

• od = than / from in this structure
• mačke = genitive singular of mačka

So the pattern is:

• X je brži od Y = X is faster than Y

Because od requires the genitive case here.

The noun changes like this:

• mačka = nominative singular
• mačke = genitive singular

So:

• mačka = cat as a subject
• od mačke = than the cat

This kind of case change is very normal in Croatian after prepositions and in comparison structures.

Here it means one cat.

That is because:

• after od in this sentence, we need the genitive singular
• the genitive singular of mačka is mačke

It is true that mačke can also be nominative plural in other contexts, but not here.

Compare:

• mačka = cat
• mačke = of the cat / cats (depending on context and grammar)
• mačaka = of cats

In this sentence, od mačke clearly means than the cat.

Because Croatian does not have articles like English a/an/the.

So a noun like zec can mean:

• a rabbit
• the rabbit

and mačka can mean:

• a cat
• the cat

The exact meaning depends on context.

That is one reason Croatian can feel more flexible than English in translation.

Kaže is 3rd person singular present tense, meaning says.

It matches djevojčica because djevojčica is singular:

• djevojčica kaže = the girl says

If the subject were plural, the verb would change.

So this is a standard subject-verb agreement pattern.

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

The neutral, natural order here is:

• Djevojčica kaže da je zec brži od mačke.

You may see other orders for emphasis, but you must still respect rules like clitic placement. For example, je still cannot just go anywhere.

So yes, Croatian allows more variation than English, but this version is the safest and most natural one for a learner.

A rough guide:

• Djevojčica ≈ dye-VOY-chee-tsa
• kaže ≈ KAH-zhe
• zec ≈ zets
• brži ≈ BR-zhee
• mačke ≈ MACH-keh

A few useful sound notes:

• č sounds like ch in church
• ž sounds like the s in measure
• c sounds like ts
• dj / đ-type sounds are softer and can be tricky for English speakers

The spelling is fairly regular in Croatian, so once you learn the letter sounds, pronunciation becomes much easier.

Usually, with a simple noun after a comparative, od + genitive is the standard choice:

• brži od mačke

You may also encounter nego in comparisons, especially when what follows is more clause-like or in certain styles, but for a sentence like this, od mačke is the most straightforward and standard option for learners.

So if you are building a basic sentence like X is faster than Y, use:

• X je brži od Y