The calm setting symbolizes the stalemate that the two sides have come to after months of uneventful fire exchanges. Each side is bored with the war and yet is unwilling to make any changes to their tactics. Although they are living in trenches, they each have warm fires to sit by and prepare their meals with and supplies of luxuries such as tea. The two camps are even close enough to each other that they hear each other talk over dinner.
The dog symbolizes the end of the rut and boredom that the soldiers feel and the escalading of conflict, an important element of the plot. The dog also symbolizes the similarities between the two groups and that the only real difference is the label that one identifies with.
The Dog of Tithwal