Vrabac kljuca malo zrno kukuruza, a dječak kroz staklo gleda njegov kljun.

Because zrno is a neuter singular noun.

The adjective mali must agree with the noun in gender, number, and case:

• masculine: mali
• feminine: mala
• neuter: malo

So:

• malo zrno = a small grain

In this sentence, zrno is also the direct object, but for a neuter inanimate noun, the accusative singular looks the same as the nominative singular, so malo zrno stays the same.

Because kukuruza is genitive singular.

Here zrno kukuruza means:

• a grain of corn
• literally: grain of corn/maize

In Croatian, a noun often goes into the genitive after another noun to show a relationship like of in English.

So:

• kukuruz = corn
• zrno kukuruza = grain of corn

Kljuca is the 3rd person singular present tense of kljucati.

It means:

• pecks
• is pecking

Depending on context, the Croatian present tense can describe:

• something happening right now
• a repeated or habitual action

So Vrabac kljuca malo zrno kukuruza can mean either:

• The sparrow is pecking at a small grain of corn
• The sparrow pecks at a small grain of corn

Vrabac is the nominative singular form, because it is the subject of the verb kljuca.

So:

• vrabac = sparrow
• it answers the question Who is pecking?
• answer: Vrabac

That is why the base subject form, nominative, is used.

A is a coordinating conjunction. In sentences like this, it often means:

• and
• while
• sometimes but, if there is a contrast

Here it connects two clauses:

• Vrabac kljuca malo zrno kukuruza
• dječak kroz staklo gleda njegov kljun

A natural sense in English is something like:

• and
• while
• whereas

So it links the sparrow’s action with the boy’s action.

The preposition kroz takes the accusative case.

So:

• kroz = through
• staklo = glass

Since staklo is a neuter singular noun, its accusative singular looks the same as its nominative singular:

• nominative: staklo
• accusative: staklo

So kroz staklo literally means through the glass.

Depending on context, English might translate it more naturally as:

• through the window
• through the pane of glass

Njegov means his, and it agrees with kljun:

• kljun is masculine singular
• so the possessive pronoun is njegov

In context, njegov kljun most naturally refers to the sparrow’s beak, not the boy’s. That is because a sparrow has a beak, and the sentence is talking about the sparrow pecking.

So:

• njegov kljun = his beak
• understood here as the sparrow’s beak

However, grammatically, njegov can sometimes be ambiguous if more than one male noun is present in the context. If you wanted to make it more explicit, Croatian could also use a phrase like:

• kljun vrapca = the sparrow’s beak

Because kljun is a masculine inanimate noun.

In Croatian, masculine nouns behave differently in the accusative depending on whether they are:

• animate
• inanimate

For masculine animate nouns, accusative singular usually looks like genitive singular. For masculine inanimate nouns, accusative singular usually looks like nominative singular.

Since kljun is inanimate:

• nominative: kljun
• accusative: kljun

So in gleda njegov kljun, the object stays kljun.

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

Whether something is definite or indefinite is usually understood from:

• context
• word order
• emphasis
• sometimes adjectives or pronouns

So:

• vrabac can mean a sparrow or the sparrow
• dječak can mean a boy or the boy
• kljun can mean a beak or the beak

English must choose an article, but Croatian usually leaves that meaning to context.

Yes. Croatian word order is more flexible than English word order because case endings already show what each word is doing.

The sentence as written is neutral and natural:

• Vrabac kljuca malo zrno kukuruza, a dječak kroz staklo gleda njegov kljun.

But other orders are possible if you want different emphasis. For example:

• Dječak kroz staklo gleda njegov kljun, a vrabac kljuca malo zrno kukuruza.

That would put the boy’s action first.

Even inside the clause, some movement is possible, but not every version sounds equally natural. Croatian word order often changes to highlight:

• topic
• focus
• contrast
• rhythm

So the original sentence is best understood as a normal, unmarked version.

It can mean both, depending on context.

Gleda is the 3rd person singular present of gledati, and Croatian present tense often covers both:

• looks
• is looking

So:

• dječak gleda njegov kljun can mean
  • the boy looks at his beak
  • the boy is looking at his beak

English often has to choose between simple present and present continuous, but Croatian usually does not make that distinction in the same way.

Because Croatian does not normally need a separate form like English is pecking or is looking.

Instead, Croatian uses the present tense and lets the context show whether the action is:

• happening now
• habitual
• descriptive

So both of these are ordinary present forms:

• kljuca = pecks / is pecking
• gleda = looks / is looking

If the context is a scene description, English often uses is pecking and is looking, but Croatian simply uses the present tense.