What is all this noise? How curious! How very curious!

From Waterloo A Near Run Thing by David Howarth. Page 124. Marvelous attention to details as recounted by the participants.

It must have been after the first charge that Mercer was ordered up to the front line on the ridge. Sir Augustus Frazer, who commanded the horse artillery, came galloping up with his face as black as a chimney sweep’s and his sleeve torn open by a musket shot. ‘Left limber up, and as fast as you can!’ he shouted. Mercer gave the order, ‘At a gallop, march!’ and away they went. (The Duke himself saw them from a distance: ‘Ah! that’s the way I like to see horse artillery move,’ he said.) Frazer rode up with Mercer, and repeated the Duke’s order: in a cavalry charge, do not expose your men but retire into the squares. Coming fresh to the ridge, Mercer noticed the air was suffocat­ingly hot like an oven, and above the roar of cannon and musketry he heard a humming noise, like myriads of black beetles on a summer night. He knew what it was, the cannon shot, the grape and musket balls. But his battery surgeon had never heard the infernal music before, and Mercer laughed at his astonishment. ‘My God, Mercer, what is that? What is all this noise? How curious! How very curious!’ And then, when a cannon shot rushed hissing past, ‘There! There! What is it all?’