If somebody moving up the latter caught the noise, it would be easy to explain it naturally.

But the wind blowing down the cup would carry it far in the enemy's direction.
There remained the risk of being heard by those parallel with the bell in the firing trenches.

Peter concluded that that trench must be very thinly held, probably only by a few observers, and the nearest might be a dozen yards off.

He had read about that being the French fashion under a big bombardment.
The next thing was to find out how to make himself known to this ally.
He decided that the only way was to surprise him.

He might get shot, but he trusted to his strength and agility against a man who was almost certainly wearied.