Noćas smo vidjeli munju, a odmah zatim čuo se grom.

Noćas refers to this night, but in English its translation depends on the tense.

• with present or future meaning: tonight
• with past meaning: last night

Because this sentence is in the past, noćas here means last night.

It is an adverb, so it does not change for case.

Croatian often leaves out subject pronouns when the verb already shows who the subject is.

In smo vidjeli, the auxiliary smo already tells you the subject is we. So mi is not necessary.

• neutral: Noćas smo vidjeli munju.
• emphatic: Noćas smo mi vidjeli munju.

Adding mi would usually give extra emphasis or contrast.

Smo is a clitic, and Croatian clitics usually go in the second position in the clause.

Here, Noćas is the first element, so smo comes right after it:

• Noćas smo vidjeli munju.

You can also say Vidjeli smo munju noćas, but that has a different rhythm or emphasis. The version in the sentence is the most natural if you want to begin with Noćas.

In the past tense, the participle agrees with the gender and number of the subject.

Since the subject is understood as we, the form depends on who we are:

• vidjeli = mixed group or all-male group
• vidjele = all-female group

So the sentence as written suggests a male or mixed group. If the speakers were all female, it would be:

Noćas smo vidjele munju...

Because they have different grammatical functions.

• munju is the direct object of vidjeli smo, so it is in the accusative
• grom is the subject of čuo se, so it is in the nominative

The base forms are:

• munja → munju in the accusative singular
• grom → grom in the nominative singular

So:

• vidjeti munju = to see lightning
• čuo se grom = thunder was heard / a thunderclap was heard

Here a is a coordinating conjunction. It often means something like and, but, or while, depending on context.

In this sentence, it connects the two events with a slight sense of transition:

• Noćas smo vidjeli munju, a odmah zatim čuo se grom.

A natural English rendering is something like:

• Last night we saw lightning, and immediately after that thunder was heard.

The comma before a is standard in Croatian.

Odmah zatim means immediately after that, right after that, or straight afterwards.

It is made of:

• odmah = immediately
• zatim = then / after that

Together they emphasize that the second event followed the first one very quickly.

Both are possible, but they do not focus on exactly the same thing.

• čuli smo grom = we heard thunder
• čuo se grom = thunder was heard / a thunderclap was heard

The first version focuses on the people hearing it. The second focuses on the sound itself as an event in the scene.

So čuo se grom sounds a bit more narrative or vivid. In everyday speech, many people might also say:

...a odmah zatim smo čuli grom.

Here se is not truly reflexive in the English sense. It does not mean the thunder somehow heard itself.

In this kind of sentence, se helps create a middle or passive-like meaning:

• čuje se = can be heard / is heard
• čuo se grom = a thunderclap was heard

This structure is very common in Croatian:

• Čula se glazba. = Music could be heard.
• Vidio se dim. = Smoke could be seen.

This is a very common learner question.

With many se-verbs in the 3rd person singular perfect, Croatian normally uses the form without visible je:

• on se rodio
• vlak se zaustavio
• čuo se grom

So čuo se is the normal standard form here.

A helpful pattern is:

• ja sam se vratio
• ti si se vratio
• on se vratio
• mi smo se vratili

Notice that in the 3rd person singular, the usual form is simply se + participle without a separate je.

Both are possible, but the emphasis is different.

• čuo se grom presents the sound as a sudden event
• grom se čuo puts more emphasis on grom

Croatian often uses this kind of word order in narration to make events feel immediate or dramatic. After odmah zatim, čuo se grom sounds especially natural and vivid.