Describe symbolism in After the Dancing Days by Margaret I. Rostkowski

In Chapter 15, Andrew uses Annie's checkerboard to symbolize the battlefield in France and to illustrate his experiences there.

"He set the checkers in two rows, facing black to red. 'The trenches lay out like this across the fields. Used to be farmers' fields, but by the time we saw them, they were ruined. Probably never be good again. So much poison... Anyway, we lived inside the trenches, like earthworms hiding from robins."'