Think of it.

Of course we knew when to run, and when to lie down.

You got so that you knew almost exactly what they'd do--if you'd been out long enough.

And then you could time what you wanted to do yourselves.
"They were a lot more nervous than we were, at the last.

They sent up enough light at night from their trenches--you know, those things that burst in the air like electric light--we had none of that to do--they did it all for us--lit up everything.