nakigoe wo kiita.

It is read なきごえ.

It comes from:

• 鳴く（なく） = to make a sound, cry, chirp, bark, etc.
• 声（こえ） = voice, sound

Together, 鳴き声 means the cry/call/sound made by an animal, bird, or insect.

を marks the direct object of the verb.

Here, the verb is 聞いた (heard / listened to), so 鳴き声を聞いた means that the cry/sound is what was heard.

So the structure is:

• 鳴き声 = the thing heard
• を = object marker
• 聞いた = heard

Japanese usually puts the verb at the end of the sentence.

So this follows a common Japanese pattern:

• object + を + verb

Here:

• 鳴き声 = object
• を = object marker
• 聞いた = verb

That word order is completely normal in Japanese.

聞いた is the plain past form of 聞く.

• 聞く = to hear / to listen / to ask
• 聞いた = heard / listened

This is the casual/plain form, not the polite form.

Compare:

• 聞いた = plain past
• 聞きました = polite past

This is a very common question.

• 聞いた focuses on the act of hearing/listening.
• 聞こえた means was audible / could be heard and often sounds more automatic or unintentional.

So:

• 鳴き声を聞いた = I heard the cry / I listened and heard it
• 鳴き声が聞こえた = I could hear a cry / a cry was audible

In many situations, both can be translated as I heard a cry, but the nuance is different.

Japanese often omits the subject when it is understood from context.

So 鳴き声を聞いた。 could mean:

• I heard a cry.
• He heard a cry.
• She heard a cry.
• They heard a cry.

The listener is expected to know who the subject is from the situation or previous sentences.

Yes, usually.

鳴き声 is most often used for the sounds made by:

• birds
• dogs
• cats
• insects
• frogs
• other animals

For a human voice, Japanese would more naturally use words like:

• 声（こえ） = voice
• 叫び声（さけびごえ） = scream/shout
• 話し声（はなしごえ） = speaking voice

So 鳴き声 strongly suggests a non-human cry or call.

Japanese does not have articles like English.

So 鳴き声 could mean:

• a cry
• the cry
• some cry/sound

The exact meaning depends on context.

That is very normal in Japanese, and learners usually need to rely on the situation rather than expecting a separate word for a/the.

By itself, it does not clearly mark singular or plural.

So 鳴き声を聞いた could mean:

• heard a cry
• heard the cry
• heard cries or the sound

Japanese often leaves number unspecified unless it matters.

Yes. It is short, but it is natural.

Japanese often allows short sentences when:

• the subject is already known
• the context is clear
• the speaker wants a simple statement

So even though English often wants something like I heard a cry, Japanese can naturally just say 鳴き声を聞いた。

Sometimes in casual conversation, object particles can be dropped, so you may hear something like:

• 鳴き声聞いた。

However, in standard Japanese, especially in writing or careful speech, を is normally included:

• 鳴き声を聞いた。

So learners should usually keep を unless they are already comfortable with casual speech patterns.