Na jednoj grani sjedi ptica, a druga grana gotovo dodiruje prozor.

Because na here means on in the sense of a fixed location, and with that meaning it normally takes the locative case.

• jedna grana = nominative, the basic dictionary form
• na jednoj grani = locative, after na for location

So:

• grana → grani
• jedna → jednoj

Both the number/adjective and the noun change because they must agree in case, gender, and number.

They have different jobs in the sentence.

In na jednoj grani, the noun comes after the preposition na, so it is in the locative: grani.

In druga grana gotovo dodiruje prozor, druga grana is the subject of the clause, so it stays in the nominative: grana.

So the contrast is:

• na jednoj grani = on one branch
• druga grana = another/the other branch

Croatian word order is much more flexible than English word order.

Both ptica sjedi and sjedi ptica are grammatically possible, but they do not sound exactly the same in emphasis.

• ptica sjedi is more neutral if you are simply saying what the bird is doing.
• na jednoj grani sjedi ptica sounds natural when describing a scene, especially after starting with the location. It is a bit like: On one branch sits a bird.

So this word order helps the sentence flow from place to action to thing/person.

Yes, sjedi is normal here.

The verb sjediti literally means to sit, but in Croatian it is also commonly used for birds when they are perched somewhere. So ptica sjedi na grani is a natural way to say that a bird is sitting/perched on a branch.

English often prefers is sitting or is perched, but Croatian can simply use sjedi.

A is a conjunction linking two clauses. It often means something like:

• and
• while
• whereas
• sometimes a mild but

Here it connects two related facts in a scene:

• one branch has a bird on it
• another branch almost touches the window

So a is not a strong contradiction here. It is more like a smooth contrast or parallel connection.

It can mean either, depending on context.

In a sentence like this, druga grana is usually understood as the other branch or another branch, not necessarily branch number two in a strict counting sense.

The pair jednoj ... druga ... works very naturally in Croatian:

• na jednoj grani = on one branch
• druga grana = the other/another branch

So it sets up a contrast between two branches.

Because druga grana is not part of the phrase on a branch. It is the subject of the second clause.

The sentence has two separate clauses:

1. Na jednoj grani sjedi ptica
2. a druga grana gotovo dodiruje prozor

In the second clause, the branch is doing the action, so no preposition is needed.

Because prozor is the direct object of the verb dodiruje (touches), and direct objects normally go in the accusative case.

For masculine inanimate nouns like prozor, the accusative singular is the same as the nominative singular:

• nominative: prozor
• accusative: prozor

So the form does not change visibly, even though the case has changed in function.

Gotovo here means almost or nearly.

It is an adverb, and it commonly goes before the verb or before the part it modifies:

• gotovo dodiruje = almost touches

That placement is very natural. It tells you the branch comes very close to the window, but does not actually touch it.

Because they are in different cases.

• jednoj agrees with grani in the locative
• druga agrees with grana in the nominative

Both words are feminine singular, but the case is different:

• nominative feminine singular: druga grana
• locative feminine singular: na drugoj grani

So drugoj would only be correct if that phrase were also after a preposition requiring the locative, for example na drugoj grani.

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

That means nouns often appear without any extra word:

• ptica
• grana
• prozor

Whether English would use a bird, the bird, a branch, or the window depends on context, not on a separate article in Croatian.

Croatian expresses definiteness in other ways, for example through context, word order, or words like jedan/jedna when needed. In this sentence, jednoj is not really just an article substitute; it genuinely means one and helps set up the contrast with druga.

Because a is joining two full clauses, each with its own predicate:

• Na jednoj grani sjedi ptica
• druga grana gotovo dodiruje prozor

In standard Croatian spelling, a comma is normally used before conjunctions like a when they connect independent clauses. So the comma here is expected and correct.