Learn Hardcore Croatian: Ključevi su ispali na pod.

auxiliary verb “biti” (to be) in the present tense: su (3rd person plural)
past participle (L-participle) of the main verb: ispali (from ispasti, to fall out)

So:
Ključevi (subject) + su (they are) + ispali (fallen) → the keys have fallen / fell.

Why is it su ispali and not je ispao or something else?

The verb must agree with the subject in number (singular/plural) and gender.

Subject: ključevi = plural masculine
Auxiliary: su = 3rd person plural of biti
Participle: ispali = masculine plural form

If it were one key, you’d say:

Ključ je ispao na pod. (singular masculine)

Here we have plural → su ispali is correct.

What is the infinitive of ispali and what exactly does ispasti mean?

The infinitive is ispasti.

Basic meanings:

ispasti = to fall out (of something), to come out, to drop out
- e.g. Ključevi su ispali iz džepa. – The keys fell out of the pocket.

Compared to:

pasti = to fall (more general, just falling down)
ispadati = imperfective counterpart of ispasti, often translated as to be falling out (repeatedly / over time).

In Ključevi su ispali na pod, ispasti suggests they fell (out / down) onto the floor as a completed event.

Why is it na pod and not na podu?

With prepositions like na (on), Croatian uses two different cases:

Accusative = movement toward somewhere
Locative = location / being at somewhere

Compare:

na pod (accusative) → onto the floor (movement)
na podu (locative) → on the floor (location, no movement)

In this sentence, the keys move and end up on the floor, so we use accusative:
Ključevi su ispali na pod. → They fell onto the floor.

What case is pod in here, and why?

Here, pod is in the accusative singular after na, because the verb expresses movement to a destination.

Nominative: pod (the floor)
Accusative: na pod (onto the floor)

Rule of thumb for na:

Where? → locative (na podu)
Where to? → accusative (na pod)

What exactly does pod mean, and when would I use alternatives like tlo or zemlja?

Pod means floor (inside a building, room, car, etc.).

Other words:

tlo = ground, soil, surface (more formal / neutral, used in geography, science)
zemlja = earth, ground, land (often outdoors, literal earth/soil, or country)

So:

Ključevi su ispali na pod. – They fell onto the floor (indoors).
Ključevi su ispali na tlo / na zemlju. – They fell onto the ground / earth (typically outdoors).

Can I change the word order, like Na pod su ispali ključevi? Does it change the meaning?

Yes, you can change word order. Croatian word order is flexible, and changes mainly emphasis, not basic meaning.

Some options:

Ključevi su ispali na pod. (neutral: what happened to the keys?)
Na pod su ispali ključevi. (emphasis on where they fell – onto the floor)
Ispali su ključevi na pod. (emphasis on the falling action)

They all describe the same event; context and intonation decide what sounds most natural.

Where does the little word su usually go, and can it move?

Su is a clitic (an unstressed short word), and Croatian clitics follow special placement rules:

In a simple sentence, the clitic usually goes in second position (after the first stressed word or phrase).

So:

Ključevi su ispali na pod. – subject first, then clitic
Na pod su ispali ključevi. – prepositional phrase first, then clitic

You can’t normally put su at the very beginning or leave it out in full sentences:

❌ Su ključevi ispali na pod.
❌ Ključevi ispali na pod. (wrong in standard Croatian as a full sentence)

How would I say “My keys fell on the floor” using this sentence?

The most natural version is to add a dative clitic for “to me / my”:

Ključevi su mi ispali na pod.
- Literally: The keys fell out on the floor to me → understood as My keys fell on the floor or I dropped my keys.

If you want to explicitly say “my keys”:

Moji su ključevi ispali na pod.
Moji ključevi su ispali na pod.

Is there a difference between su ispali and something like su pali?

Yes, there is a nuance:

pasti → pali (past participle)
- more general: they fell (just the act of falling)
ispasti → ispali
- more specific: they fell out / dropped out / ended up down

In many contexts they overlap, but:

Ključevi su ispali na pod. suggests they kind of fell out (of your pocket / hand) onto the floor.
Ključevi su pali na pod. sounds a bit more neutral: they simply fell onto the floor.

Both are understandable; ispali is very common for keys, coins, etc. “falling out” of somewhere.

How do I pronounce ključevi, especially the lj and če parts?

Pronunciation tips:

klj – said together, not as three separate sounds.
lj – a palatal l, similar to the lli in million (AmE) or lli in million (BrE).
č – like ch in church (a hard “ch”).

Syllables: klju‑če‑vi
Stress is usually on the first syllable: KLJU‑če‑vi.

Could I say this in the present tense, like “The keys are falling on the floor”? How?

Yes, you can, but you’d use the imperfective verb padati:

Ključevi padaju na pod. – The keys are falling onto the floor.

Or, if you want “are falling out”:

Ključevi ispadaju na pod. – The keys are (in the process of) falling out onto the floor.

In your original sentence, su ispali describes a completed past event.