"That's a nice song" said young Sam, and Vimes remembered that he was hearing it for the first time.
"It's an old soldiers' song", he said.
"Really, sarge? But it's about angels."
Yes, thought Vimes, and it's amazing what bits those angels cause to rise up as the song progresses. It's a real soldiers' song: sentimental, with dirty bits.
"As I recall, they used to sing it after battles" he said. "I've seen old men cry when they sing it" he added.
"Why? It sounds cheerful."
They were remembering who they were not singing it with, thought Vimes. You'll learn. I know you will.