Well, there are a few different symbols in "Two Friends." One is the rumbling in the background from the cannon's firing, which is also Mount Valerien erupting. This continuous "eruption" helps to build the rising action and symbolizes the doom that is ahead (foreshadowing). In addition, the fish that is caught by the two friends and then essentially becomes similar to their own fate is also symbolic. The two men end up floating dead in the water while the Prussian soldiers consume the fish that kept and brought the two friends together in the first place. A bit ironic.