Learn Hardcore Spanish (Spain): Cuando volvió a sonar el silbato, todos guardamos silencio un segundo. - When the whistle sounded again, we all stayed silent for a second.

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

Why does volvió a sonar mean sounded again?

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

So:

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

A few similar examples:

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

Why is there an a in volvió a sonar?

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

So:

You cannot normally leave the a out here.