The noise seemed to die away.

It did not cease for there was still a good deal of talking, but there was no more shouting, until there was a sudden whirring sound.
"An aeroplane!" whispered Boris.

"I've seen them for the last few days, flying in all directions.

They use them for scouting." "I knew I ought to recognize that sound!" said Fred.
It seemed fairly safe for them to speak to one another now.

For some reason it was quite evident they had been forgotten.
There was an interval of almost complete silence; then came a sudden explosion of orders.