Cuando volvió a sonar el silbato, todos guardamos silencio un segundo.

This uses the very common pattern volver a + infinitive, which means to do something again.

So:

• volvió = he/she/it came back / returned
• volvió a sonar = rang again / sounded again

In this sentence, el silbato volvió a sonar means the whistle sounded again.

A few similar examples:

• Volvió a llamar = He/She called again
• Volvimos a intentarlo = We tried again
• ¿Puedes volver a explicarlo? = Can you explain it again?

So it is not really about physically returning here; it is a grammar structure meaning again.

After volver in this structure, Spanish requires a before the infinitive:

• volver a + infinitive

So:

• volver a comer = to eat again
• volver a empezar = to start again
• volver a sonar = to sound again

You cannot normally leave the a out here.

Because after volver a, the next verb stays in the infinitive.

That is the standard structure:

• volvió a sonar
• volvieron a entrar
• volvimos a hablar

This is similar to English structures like want to go or need to leave, where one conjugated verb is followed by another verb in a basic form.

Here:

• volvió is the conjugated verb
• sonar is the infinitive

They are in the preterite because the sentence describes completed actions in a story:

• volvió = it sounded again
• guardamos = we fell silent / we kept silent

The preterite is commonly used for actions that happen as single events in a sequence.

This sentence feels like a narrative moment:

1. the whistle sounded again
2. everyone was silent for a second

If the sentence used the imperfect, it would suggest ongoing background action instead of a completed event.

Yes, guardamos can be either:

• present: we keep
• preterite: we kept

For -ar verbs, the nosotros form is the same in the present and the preterite.

So guardamos can mean either one depending on context.

Here, the context clearly makes it preterite:

• it is a past narrative sentence
• it follows volvió, which is also in the past
• un segundo fits a completed action in the story

So here it means we kept / fell silent, not we keep.

Because cuando can be followed by different past tenses depending on the meaning.

Here, cuando volvió a sonar el silbato refers to a specific completed event: the moment when the whistle sounded again.

That is why the preterite fits well.

Compare:

• Cuando volvió a sonar el silbato, todos guardamos silencio.
  = a specific event in a story

• Cuando sonaba el silbato, todos guardábamos silencio.
  = something habitual or repeated in the past

So the choice of tense depends on whether the speaker means a one-time event or a repeated/background situation.

Guardar silencio is a set expression meaning:

• to keep silent
• to remain silent
• sometimes more naturally in English, to fall silent

Literally, guardar often means to keep, to store, or to put away, but in this expression it means to maintain silence.

So:

• Todos guardamos silencio = We all kept silent / fell silent

It is a fairly natural and standard expression in Spanish.

Both can work, but they are not exactly the same.

• guardar silencio = to remain/keep silent
• callarse = to be quiet / to stop talking / to shut up

Guardar silencio often sounds a bit more neutral, descriptive, or narrative.
Callarse can sometimes feel more direct or more focused on stopping speech.

Compare:

• Todos guardamos silencio un segundo.
  = We all fell silent for a second.

• Todos nos callamos un segundo.
  = We all went quiet for a second.

The second one is possible, but guardar silencio sounds a little more literary or formal.

Spanish usually leaves out subject pronouns when the verb already shows who the subject is.

So guardamos already tells you we.

Also, todos already helps identify the group:

• todos guardamos silencio = we all fell silent

You could say todos nosotros, but it is usually unnecessary unless you want emphasis or contrast.

For example:

• Todos guardamos silencio = normal
• Todos nosotros guardamos silencio, pero ellos no = emphatic contrast

Yes.

Because the verb is guardamos = we, the speaker is part of the group.

So todos here means all of us or everyone present, including me/us.

If the speaker wanted to describe a group that did not include them, the sentence would use a different verb form, for example:

• todos guardaron silencio = they all fell silent

In Spanish, expressions of duration often appear without a preposition.

So:

• un segundo = for a second
• dos horas = for two hours
• toda la tarde = all afternoon

That means:

• guardamos silencio un segundo = we kept silent for a second

You may also hear por un segundo in some contexts, but here plain un segundo is the most natural way to express duration.

Usually, yes.

El silbato most commonly means whistle, especially the kind used by:

• referees
• teachers
• coaches
• police officers
• lifeguards

Since the verb is sonar (to sound / to ring), the whistle is the most natural reading here.

Yes. Spanish allows flexible word order.

You could also say:

• Todos guardamos silencio un segundo cuando volvió a sonar el silbato.

That means essentially the same thing.

Putting cuando volvió a sonar el silbato first gives a slightly more narrative feel and highlights the trigger for what happened next.

The comma is natural when the cuando clause comes first:

• Cuando volvió a sonar el silbato, todos guardamos silencio un segundo.

When the cuando clause comes second, the comma is often omitted:

• Todos guardamos silencio un segundo cuando volvió a sonar el silbato.