Learn Hardcore Croatian: Ona često sluša glazbu u autobusu. - She often listens to music on the bus.

Because slušati takes a direct object in the accusative case. Glazba is the nominative (dictionary form), and feminine -a nouns change -a to -u in the accusative singular: glazba → glazbu (like knjiga → knjigu, pjesma → pjesmu).

Why is it u autobusu and not autobusom or na autobusu?

u autobusu = in the bus (inside it). It uses the preposition u with the locative case for location.
autobusom = by bus (as a means of transport): Ide na posao autobusom.
na autobusu = on the bus (physically on top of it) or “on a bus” as an object (e.g., working on a bus), not as a passenger.

Why is it autobusu and not autobus after u?

With u meaning “in/inside,” Croatian uses the locative case, and masculine nouns like autobus take the ending -u in the locative singular: autobusu. If you said u autobus (accusative), it would mean “into the bus” (motion): Ulazi u autobus.

Can I leave out Ona?

Yes. Croatian is a pro‑drop language: the verb ending (sluša = 3rd person singular) shows the subject. Često sluša glazbu u autobusu. is perfectly natural. Keep ona for emphasis or contrast.

Where can često go in the sentence?

Adverbs are flexible:

Neutral: Ona često sluša glazbu u autobusu. / Često sluša glazbu u autobusu.
Emphasis on place: U autobusu često sluša glazbu.
Combined focus: Često u autobusu sluša glazbu. Placing često at the very end is less common.

Does the present tense sluša mean a habitual action or something happening right now?

Both are possible in Croatian. The adverb često makes it clearly habitual here. Without a time adverb, Ona sluša glazbu can mean either “She listens to music (generally)” or “She is listening to music (now).”

What’s the difference between slušati and čuti?

slušati = to listen (intentional action).
čuti = to hear (perceive sound). Example: Čujem buku, ali ne slušam glazbu.

Should there be a reflexive se (like sluša se)?

No. Slušati isn’t reflexive in the meaning “to listen (to something).” Sluša se can occur impersonally/passively in other contexts (“is being listened to”), but not here.

Can I use muzika instead of glazba?

In standard Croatian, glazba is preferred, but muzika is widely understood and used informally. In Serbian/Bosnian, muzika is standard. Grammar is the same: slušati glazbu/muziku.

Why doesn’t Croatian use articles like “a/the” here?

Croatian has no articles. Definiteness comes from context or determiners:

u tom autobusu = in that bus
u jednom autobusu = in a/one bus Without them, u autobusu can mean either “on the bus” or “on a bus.”

How do I pronounce the special letters?

č = “ch” in “church”: često ≈ CHEH-stoh
š = “sh” in “ship”: sluša ≈ SLOO-sha
u = “oo” in “food”: u autobusu ≈ oo ow-toh-BOO-soo
z in glazbu is plain “z.”

Is u busu acceptable instead of u autobusu?

Yes. Bus is a common colloquial shortening. Locative singular: u busu. Autobus sounds more formal or neutral.

Could I front the object and say Glazbu često sluša u autobusu?

Yes. Croatian allows relatively free word order for emphasis. Glazbu često sluša u autobusu emphasizes glazbu (“music”) more than the neutral (Ona) često sluša glazbu u autobusu.

What’s the present-tense conjugation of slušati?

ja: slušam
ti: slušaš
on/ona/ono: sluša
mi: slušamo
vi: slušate
oni/one/ona: slušaju