Iznenadilo me da je vlak stigao na vrijeme.

Because iznenadilo agrees with the whole clause da je vlak stigao na vrijeme.

In Croatian, when an entire event or fact is the thing that surprises someone, it is very common to use neuter singular in the main verb:

• Iznenadilo me da... = It surprised me that...

So the hidden subject is basically to/that fact, which is treated as neuter singular.

Compare:

• Iznenadio me vlak. = The train surprised me.
  Here vlak is masculine, so you get iznenadio.
• Iznenadilo me da je vlak stigao na vrijeme. = It surprised me that the train arrived on time.
  Here the subject is the whole clause, so iznenadilo is neuter.

Me is the unstressed form of the pronoun ja in the accusative case.

The verb iznenaditi takes a direct object meaning the person who is surprised:

• Iznenadilo me = It surprised me

Here are the forms:

• ja = I
• mene / me = me

Why me specifically? Because Croatian often uses short, unstressed clitic pronouns in normal sentence flow.

Compare:

• Iznenadilo me. = neutral, natural
• Iznenadilo mene. = more emphatic, like It surprised me (not someone else)

So me is the normal choice here.

Here da introduces a subordinate clause, similar to English that:

• Iznenadilo me da je vlak stigao na vrijeme.
• It surprised me that the train arrived on time.

So da je vlak stigao na vrijeme is the content of what surprised the speaker.

This da is very common after verbs and expressions involving:

• saying
• knowing
• seeing
• feeling
• being surprised

Examples:

• Znam da dolazi. = I know that he/she is coming.
• Drago mi je da si ovdje. = I’m glad that you’re here.
• Čudi me da kasni. = I’m surprised that he/she is late.

This is because je is a clitic in Croatian, and clitics usually go in second position in their clause.

In the subordinate clause:

• da = first element
• je = clitic, so it comes right after that
• vlak stigao na vrijeme follows

So:

• da je vlak stigao na vrijeme

This is normal Croatian word order.

You may also see word order shifts in other contexts, but this structure is very standard. The key point is that je is not behaving like a fully stressed independent word here.

Je stigao is the perfect tense in Croatian.

It is formed with:

• the present tense of biti (je)
• the l-participle of the main verb (stigao)

So:

• je stigao = has arrived / arrived

In this sentence, English usually translates it as a simple past:

• the train arrived on time

Croatian uses the perfect very widely for completed past events.

Stigao is the masculine singular past participle form, and it agrees with vlak.

Since:

• vlak = train
• vlak is masculine singular

the participle must also be masculine singular:

• vlak je stigao

Compare:

• autobus je stigao — masculine singular
• pošta je stigla — feminine singular
• pismo je stiglo — neuter singular
• vlakovi su stigli — masculine plural

So stigao is chosen because it matches vlak.

The verb here is stići, which is perfective.

• stići = to arrive, to get there, to reach
• stizati = imperfective partner, meaning something like to be arriving / to arrive regularly / to manage to get somewhere in an ongoing or repeated sense

In this sentence, a completed single event is meant:

• the train arrived

So stići is the natural choice:

• vlak je stigao

If you used stizao, it would suggest repeated, habitual, or ongoing background meaning, which does not fit as well here.

Na vrijeme is the standard expression for on time.

So:

• stići na vrijeme = to arrive on time

This is a fixed and very common phrase.

By contrast, u vrijeme usually means something more like:

• in time
• during the time of
• at the time of

Examples:

• Stigao je na vrijeme. = He arrived on time.
• Stigao je u pravo vrijeme. = He arrived at the right time.
• U vrijeme rata... = During the war...

So for punctuality, use na vrijeme.

Vlak is in the nominative case because it is the subject of the subordinate clause:

• da je vlak stigao na vrijeme

The train is the thing that arrived, so it is the subject.

If you look at the clause structure:

• je stigao = arrived
• vlak = who/what arrived? → the train

That makes it nominative.

Yes. That is also grammatically correct.

Both are possible:

• Iznenadilo me da je vlak stigao na vrijeme.
• Iznenadilo me je da je vlak stigao na vrijeme.

The difference is mainly stylistic and rhythmic. In everyday Croatian, clitics are often kept short and compact, so Iznenadilo me da... sounds very natural.

Adding je in the main clause can sound a bit more explicit or formal in some contexts, but it is not a major meaning difference.

The sentence is fairly flexible, but not completely free.

The neutral version is:

• Iznenadilo me da je vlak stigao na vrijeme.

You can sometimes move elements around for emphasis, but Croatian still follows important rules, especially with clitics like me and je.

For example, the subordinate clause could be fronted:

• Da je vlak stigao na vrijeme, iznenadilo me.

This is possible, but it sounds more marked and literary or contrastive. The original order is the most natural in normal conversation and writing.

Sometimes yes, but da is the more neutral and standard choice here.

You may hear or read:

• Iznenadilo me što je vlak stigao na vrijeme.

This is also understandable and natural in many contexts. The difference is subtle, and usage can vary by speaker, region, and style.

A simple way to think about it:

• da is very common after verbs introducing a fact or statement
• što can also introduce a content clause, often with a slightly different stylistic feel

For a learner, Iznenadilo me da... is an excellent standard model.

It is very similar to English in meaning, but the grammar often looks slightly different.

Croatian can say:

• Vlak me iznenadio. = The train surprised me.
• Iznenadilo me da je vlak stigao na vrijeme. = It surprised me that the train arrived on time.

So Croatian often uses:

• a thing/person as subject
• the surprised person in the accusative
• or a whole clause as the subject-like idea

The biggest difference for English speakers is usually not meaning, but the form:

• agreement in iznenadilo
• use of clitics like me
• use of da to introduce the clause