Μετά τη δεύτερη βροντή, η γάτα κρύφτηκε κάτω από το κρεβάτι, γιατί φοβήθηκε την αστραπή.

Because δεύτερη βροντή is a feminine singular phrase in the accusative, and the feminine accusative article is την. In Modern Greek, that final -ν is often dropped before many consonants, so την becomes τη.

So:

• full form: την δεύτερη βροντή
• very common shorter form: τη δεύτερη βροντή

Both are understandable, but τη is very natural here.

Because it has to agree with βροντή, and βροντή is a feminine noun.

Greek adjectives change form to match the noun in:

• gender
• number
• case

Here:

• βροντή = feminine, singular
• after μετά it is in the accusative
• so δεύτερη also appears in the feminine singular accusative form

That is why you get τη δεύτερη βροντή.

Βροντή means thunder, but in a sentence like this it often sounds more like a thunderclap or a peal of thunder in English.

So μετά τη δεύτερη βροντή is naturally understood as:

• after the second thunderclap
• or after the second peal of thunder

Yes. In Greek, the definite article is used much more regularly than in English. So η γάτα simply means the cat, and it is the normal way to say it.

Also, η γάτα is in the nominative, because it is the subject of the verb κρύφτηκε.

So:

• η γάτα = the cat as subject
• τη/την γάτα = the cat as object

They are both in the aorist, which is the most common Greek past tense for a single completed event.

So:

• κρύφτηκε = hid
• φοβήθηκε = got scared / became afraid

The aorist does not focus on duration. It just presents each action as a whole event in the past.

That fits this sentence well:

1. there was a second thunderclap
2. the cat hid
3. it got scared of the lightning

Because κρύφτηκε means hid itself / hid, while έκρυψε means hid something.

Compare:

• κρύβω = I hide something
• κρύβομαι = I hide / I hide myself

The form κρύφτηκε comes from κρύβομαι, so it is the correct choice for the cat hid.

If you said η γάτα έκρυψε..., it would mean the cat hid something.

Because Greek often drops subject pronouns when they are already clear from the verb form and the context.

Here, φοβήθηκε means he/she/it got scared. Since the subject is still the cat, Greek does not need to repeat η γάτα or add a separate word for it.

So Greek naturally says:

• η γάτα κρύφτηκε ... γιατί φοβήθηκε ...

Literally, that is something like:

• the cat hid ... because got scared ...

But in natural English, we add it:

• the cat hid ... because it got scared ...

This is a very common Greek expression meaning under the bed.

It breaks down like this:

• κάτω = down / below
• από = from, but in this expression it helps form under
• το κρεβάτι = the bed in the accusative form

Together:

• κάτω από το κρεβάτι = under the bed

Even though από often means from, in set phrases like κάτω από, πάνω από, and μέσα από, it combines with another word to create a location or movement expression.

Because κρεβάτι is a neuter noun, and many neuter nouns in Modern Greek have the same form in the nominative and accusative singular.

So:

• το κρεβάτι = nominative singular
• το κρεβάτι = accusative singular

The article and noun look the same in both cases.

Yes. Γιατί can mean both:

• why?
• because

The meaning depends on context.

Here it clearly means because, since it introduces the reason the cat hid:

• γιατί φοβήθηκε την αστραπή = because it got scared of the lightning

If it were a question, the intonation or a question mark would make that clear.

Greek also has επειδή for because, but γιατί is very common in everyday language.

It is την αστραπή because αστραπή is a feminine noun in the accusative, and it is the object of φοβήθηκε.

Also, the full article την is normally kept before a vowel, and αστραπή begins with α.

So:

• τη βροντή is common before a consonant
• την αστραπή is natural before a vowel

Also note the meaning:

• αστραπή = lightning or flash of lightning

That is just how the verb works in Greek.

Φοβάμαι / φοβήθηκα often takes the thing feared as a direct object in the accusative:

• φοβάμαι τα σκυλιά = I’m afraid of dogs
• φοβήθηκε την αστραπή = it got scared of the lightning

So even though English usually says afraid of something, Greek often uses the accusative directly.

Yes. Both are possible:

• μετά τη δεύτερη βροντή
• μετά από τη δεύτερη βροντή

In Modern Greek, μετά από is extremely common in everyday speech, while μετά on its own is also correct and often feels a bit more compact or slightly more formal/written.

So the sentence as given is perfectly natural, but μετά από would also be normal.

Greek word order is more flexible than English word order, because the endings and articles show what each word is doing.

This sentence uses a very natural order:

• Μετά τη δεύτερη βροντή = time setting
• η γάτα = subject
• κρύφτηκε = main action
• κάτω από το κρεβάτι = place
• γιατί φοβήθηκε την αστραπή = reason

You could rearrange parts of it for emphasis, but the given version is clear and idiomatic. For a learner, it is a very good model to follow.